Primary 4 Mathematics · Chapter 3 · Answers and explanations

Lesson 3.1: Multiplication by a 1-Digit Number (answers)

Section A · Multiple choice 4 marks

1. What is 47 × 3?1 mark

(A) 121(B) 141(C) 131(D) 241

Answer: (B) 141Ones: 7 × 3 = 21, write 1 and regroup 2 tens. Tens: 4 × 3 + 2 = 14, write 14. So 47 × 3 = 141.

2. What is 258 × 4?1 mark

(A) 802(B) 1,132(C) 1,032(D) 932

Answer: (C) 1,032Ones: 8 × 4 = 32, write 2 and regroup 3 tens. Tens: 5 × 4 + 3 = 23, write 3 and regroup 2 hundreds. Hundreds: 2 × 4 + 2 = 10, write 10. So 258 × 4 = 1,032.

3. What is 306 × 5?1 mark

(A) 1,500(B) 1,560(C) 2,030(D) 1,530

Answer: (D) 1,530Ones: 6 × 5 = 30, write 0 and regroup 3 tens. Tens: 0 × 5 + 3 = 3, write 3. Hundreds: 3 × 5 = 15, write 15. So 306 × 5 = 1,530.

4. What is 480 × 7?1 mark

(A) 3,360(B) 2,860(C) 336(D) 3,460

Answer: (A) 3,360Multiply 48 × 7 first, then write the zero. 8 × 7 = 56, write 6 and regroup 5. 4 × 7 + 5 = 33, write 33. So 48 × 7 = 336. Now 480 is 48 tens, so 480 × 7 = 3,360.

Section B · Write your answer 11 marks

5. What is 64 × 5?1 mark

Answer: 320Ones: 4 × 5 = 20, write 0 and regroup 2 tens. Tens: 6 × 5 + 2 = 32, write 32. So 64 × 5 = 320.

6. What is 128 × 7?1 mark

Answer: 896Ones: 8 × 7 = 56, write 6 and regroup 5 tens. Tens: 2 × 7 + 5 = 19, write 9 and regroup 1 hundreds. Hundreds: 1 × 7 + 1 = 8, write 8. So 128 × 7 = 896.

7. What is 709 × 6?1 mark

Answer: 4,254Ones: 9 × 6 = 54, write 4 and regroup 5 tens. Tens: 0 × 6 + 5 = 5, write 5. Hundreds: 7 × 6 = 42, write 42. So 709 × 6 = 4,254.

8. Find the product of 85 and 9.1 mark

Answer: 765Ones: 5 × 9 = 45, write 5 and regroup 4 tens. Tens: 8 × 9 + 4 = 76, write 76. So 85 × 9 = 765.

9. A bus can carry 56 passengers. How many passengers can 8 buses carry?1 mark

Answer: 448Equal groups, so multiply. Ones: 6 × 8 = 48, write 8 and regroup 4 tens. Tens: 5 × 8 + 4 = 44, write 44. So 56 × 8 = 448. 8 buses carry 448 passengers.

10. A shop sells 245 pens each day for 4 days. On the fifth day it sells 190 pens. How many pens does it sell in the 5 days?2 marks

Answer: 1,170Pens in 4 days: 245 × 4 = 980 (5 × 4 = 20, write 0 regroup 2; 4 × 4 + 2 = 18, write 8 regroup 1; 2 × 4 + 1 = 9). Add the fifth day: 980 + 190 = 1,170. It sells 1,170 pens.

11. A pack has 36 sweets. Mei buys 8 packs and gives away 59 sweets. How many sweets does she have left?2 marks

Answer: 229Sweets in 8 packs: 36 × 8 = 288 (6 × 8 = 48, write 8 regroup 4; 3 × 8 + 4 = 28). Take away 59: 288 − 59 = 229. She has 229 sweets left.

12. Ravi saves $85 each month for 6 months. He then buys a bicycle for $389. How much money does he have left?2 marks

Answer: $121Money saved: 85 × 6 = 510 (5 × 6 = 30, write 0 regroup 3; 8 × 6 + 3 = 51). Money left: $510 − $389 = $121.

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Primary 4 Mathematics · Chapter 3 · Answers and explanations

Lesson 3.2: Multiplication of 4-Digit Numbers (answers)

Section A · Multiple choice 4 marks

1. What is 2,345 × 4?1 mark

(A) 8,260(B) 10,380(C) 9,380(D) 9,280

Answer: (C) 9,380Ones: 5 × 4 = 20, write 0 and regroup 2 tens. Tens: 4 × 4 + 2 = 18, write 8 and regroup 1 hundreds. Hundreds: 3 × 4 + 1 = 13, write 3 and regroup 1 thousands. Thousands: 2 × 4 + 1 = 9, write 9. So 2,345 × 4 = 9,380.

2. What is 3,068 × 5?1 mark

(A) 15,000(B) 15,040(C) 16,340(D) 15,340

Answer: (D) 15,340Ones: 8 × 5 = 40, write 0 and regroup 4 tens. Tens: 6 × 5 + 4 = 34, write 4 and regroup 3 hundreds. Hundreds: 0 × 5 + 3 = 3, write 3. Thousands: 3 × 5 = 15, write 15. So 3,068 × 5 = 15,340.

3. What is 4,005 × 7?1 mark

(A) 28,035(B) 28,005(C) 24,535(D) 280,350

Answer: (A) 28,035Ones: 5 × 7 = 35, write 5 and regroup 3 tens. Tens: 0 × 7 + 3 = 3, write 3. Hundreds: 0 × 7 = 0, write 0. Thousands: 4 × 7 = 28, write 28. So 4,005 × 7 = 28,035.

4. Round 2,987 to the nearest thousand to estimate 2,987 × 4. What is the estimate?1 mark

(A) 8,000(B) 12,000(C) 16,000(D) 1,200

Answer: (B) 12,0002,987 is close to 3,000. Estimate: 3,000 × 4 = 12,000. (Wrong answers come from rounding down to 2,000, rounding up to 4,000, or losing zeros.)

Section B · Write your answer 11 marks

5. What is 1,526 × 6?1 mark

Answer: 9,156Ones: 6 × 6 = 36, write 6 and regroup 3 tens. Tens: 2 × 6 + 3 = 15, write 5 and regroup 1 hundreds. Hundreds: 5 × 6 + 1 = 31, write 1 and regroup 3 thousands. Thousands: 1 × 6 + 3 = 9, write 9. So 1,526 × 6 = 9,156.

6. What is 5,208 × 3?1 mark

Answer: 15,624Ones: 8 × 3 = 24, write 4 and regroup 2 tens. Tens: 0 × 3 + 2 = 2, write 2. Hundreds: 2 × 3 = 6, write 6. Thousands: 5 × 3 = 15, write 15. So 5,208 × 3 = 15,624.

7. Round 4,078 to the nearest thousand to estimate 4,078 × 5. What is the estimate?1 mark

Answer: 20,0004,078 is close to 4,000. Estimate: 4,000 × 5 = 20,000. (The exact answer is 20,390, so the estimate is close.)

8. What is 7,040 × 8?1 mark

Answer: 56,320Ones: 0 × 8 = 0, write 0. Tens: 4 × 8 = 32, write 2 and regroup 3 hundreds. Hundreds: 0 × 8 + 3 = 3, write 3. Thousands: 7 × 8 = 56, write 56. So 7,040 × 8 = 56,320.

9. What is the product of 9,999 and 2?1 mark

Answer: 19,998Ones: 9 × 2 = 18, write 8 and regroup 1 tens. Tens: 9 × 2 + 1 = 19, write 9 and regroup 1 hundreds. Hundreds: 9 × 2 + 1 = 19, write 9 and regroup 1 thousands. Thousands: 9 × 2 + 1 = 19, write 19. So 9,999 × 2 = 19,998.

10. A factory makes 1,740 toys every day. Round 1,740 to the nearest thousand to estimate the toys made in 6 days. Then find the exact number.2 marks

Answer: Estimate 12,000; exact 10,4401,740 rounds to 2,000. Estimate: 2,000 × 6 = 12,000. Exact: Ones: 0 × 6 = 0, write 0. Tens: 4 × 6 = 24, write 4 and regroup 2 hundreds. Hundreds: 7 × 6 + 2 = 44, write 4 and regroup 4 thousands. Thousands: 1 × 6 + 4 = 10, write 10. So 1,740 × 6 = 10,440. The estimate is a little higher because we rounded up.

11. A stadium has 8 blocks. Each block has 1,250 seats. 3,764 seats are taken. How many seats are empty?2 marks

Answer: 6,236All seats: 1,250 × 8 = 10,000 (0 × 8 = 0; 5 × 8 = 40, write 0 regroup 4; 2 × 8 + 4 = 20; 1 × 8 + 2 = 10). Empty seats: 10,000 − 3,764 = 6,236.

12. A shop had 10,000 eggs. It sold 2,375 eggs each day for 4 days. How many eggs are left?2 marks

Answer: 500Eggs sold: 2,375 × 4 = 9,500 (5 × 4 = 20, write 0 regroup 2; 7 × 4 + 2 = 30, write 0 regroup 3; 3 × 4 + 3 = 15, write 5 regroup 1; 2 × 4 + 1 = 9). Eggs left: 10,000 − 9,500 = 500.

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Primary 4 Mathematics · Chapter 3 · Answers and explanations

Lesson 3.3: Multiplication by a 2-Digit Number (answers)

Section A · Multiple choice 4 marks

1. What is 53 × 20?1 mark

(A) 106(B) 10,600(C) 73(D) 1,060

Answer: (D) 1,060Multiply by 2 first: 53 × 2 = 106. Then multiply by 10 to make it × 20: 1,060.

2. What is 34 × 12?1 mark

(A) 408(B) 102(C) 68(D) 508

Answer: (A) 408Step 1 (ones): 34 × 2 = 68. Step 2 (tens): 34 × 10 = 340 (because 34 × 1 = 34, then × 10). Add: 68 + 340 = 408.

3. What is 215 × 14?1 mark

(A) 1,075(B) 3,010(C) 860(D) 3,110

Answer: (B) 3,010Step 1 (ones): 215 × 4 = 860. Step 2 (tens): 215 × 10 = 2,150 (because 215 × 1 = 215, then × 10). Add: 860 + 2,150 = 3,010.

4. What is 126 × 35?1 mark

(A) 1,008(B) 630(C) 4,410(D) 4,510

Answer: (C) 4,410Step 1 (ones): 126 × 5 = 630. Step 2 (tens): 126 × 30 = 3,780 (because 126 × 3 = 378, then × 10). Add: 630 + 3,780 = 4,410.

Section B · Write your answer 11 marks

5. What is 60 × 30?1 mark

Answer: 1,8006 × 3 = 18. There are two zeros in 60 × 30, so the answer is 1,800.

6. What is 47 × 13?1 mark

Answer: 611Step 1 (ones): 47 × 3 = 141. Step 2 (tens): 47 × 10 = 470 (because 47 × 1 = 47, then × 10). Add: 141 + 470 = 611.

7. What is 235 × 20?1 mark

Answer: 4,700235 × 2 = 470. Then × 10 gives 4,700.

8. What is 68 × 45?1 mark

Answer: 3,060Step 1 (ones): 68 × 5 = 340. Step 2 (tens): 68 × 40 = 2,720 (because 68 × 4 = 272, then × 10). Add: 340 + 2,720 = 3,060.

9. What is 312 × 24?1 mark

Answer: 7,488Step 1 (ones): 312 × 4 = 1,248. Step 2 (tens): 312 × 20 = 6,240 (because 312 × 2 = 624, then × 10). Add: 1,248 + 6,240 = 7,488.

10. A hall has 28 rows of chairs with 35 chairs in each row. 94 chairs are empty. How many chairs are used?2 marks

Answer: 886Chairs in the hall: 28 × 35. Step 1 (ones): 35 × 8 = 280. Step 2 (tens): 35 × 20 = 700 (because 35 × 2 = 70, then × 10). Add: 280 + 700 = 980. (Here 35 is multiplied by 8 and then by 20.) Chairs used: 980 − 94 = 886.

11. Mei reads 24 pages a day for 15 days. Her book has 400 pages. How many pages does she still have to read?2 marks

Answer: 40Pages read: 24 × 15 = 360 (24 × 5 = 120, 24 × 10 = 240, 120 + 240 = 360). Pages left: 400 − 360 = 40.

12. Ravi buys 32 packets of stickers at $15 each. He sells all the packets at $19 each. How much profit does he make?2 marks

Answer: $128Cost: 32 × 15 = 480 (32 × 5 = 160, 32 × 10 = 320). Sales: 32 × 19 = 608 (32 × 9 = 288, 32 × 10 = 320). Profit = $608 − $480 = $128.

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Primary 4 Mathematics · Chapter 3 · Answers and explanations

Lesson 3.4: Division by a 1-Digit Number (answers)

Section A · Multiple choice 4 marks

1. Find the quotient and the remainder of 85 ÷ 4.1 mark

(A) Quotient 21; remainder 1(B) Quotient 1; remainder 21(C) Quotient 22; remainder 1(D) Quotient 21; remainder 3

Answer: (A) Quotient 21; remainder 18 ÷ 4 = 2. Bring down 5 to make 5. 5 ÷ 4 = 1 r 1. So 85 ÷ 4 = 21 remainder 1.

2. What is 672 ÷ 8?1 mark

(A) 48(B) 84(C) 804(D) 94

Answer: (B) 846 is smaller than 8, so use the next digit too. 67 ÷ 8 = 8 r 3. Bring down 2 to make 32. 32 ÷ 8 = 4. So 672 ÷ 8 = 84.

3. What is the remainder when 487 is divided by 6?1 mark

(A) 81(B) 4(C) 1(D) 2

Answer: (C) 14 is smaller than 6, so use the next digit too. 48 ÷ 6 = 8. Bring down 7 to make 7. 7 ÷ 6 = 1 r 1. So 487 ÷ 6 = 81 remainder 1. The remainder is 1. (81 is the quotient, not the remainder.)

4. A rope 250 cm long is cut into pieces of 8 cm each. How many full pieces can be cut?1 mark

(A) 32(B) 2(C) 30(D) 31

Answer: (D) 312 is smaller than 8, so use the next digit too. 25 ÷ 8 = 3 r 1. Bring down 0 to make 10. 10 ÷ 8 = 1 r 2. So 250 ÷ 8 = 31 remainder 2. We only count full pieces, so the answer is the quotient, 31. The 2 cm left over is not enough for another piece.

Section B · Write your answer 11 marks

5. What is 96 ÷ 4?1 mark

Answer: 249 ÷ 4 = 2 r 1. Bring down 6 to make 16. 16 ÷ 4 = 4. So 96 ÷ 4 = 24.

6. Find the quotient and the remainder of 75 ÷ 6.1 mark

Answer: Quotient 12; remainder 37 ÷ 6 = 1 r 1. Bring down 5 to make 15. 15 ÷ 6 = 2 r 3. So 75 ÷ 6 = 12 remainder 3.

7. What is 804 ÷ 4?1 mark

Answer: 2018 ÷ 4 = 2. Bring down 0 to make 0. 0 ÷ 4 = 0 (write 0). Bring down 4 to make 4. 4 ÷ 4 = 1. So 804 ÷ 4 = 201. Remember to write the 0 in the quotient.

8. Find the quotient and the remainder of 925 ÷ 6.1 mark

Answer: Quotient 154; remainder 19 ÷ 6 = 1 r 3. Bring down 2 to make 32. 32 ÷ 6 = 5 r 2. Bring down 5 to make 25. 25 ÷ 6 = 4 r 1. So 925 ÷ 6 = 154 remainder 1.

9. What is 354 ÷ 6?1 mark

Answer: 593 is smaller than 6, so use the next digit too. 35 ÷ 6 = 5 r 5. Bring down 4 to make 54. 54 ÷ 6 = 9. So 354 ÷ 6 = 59.

10. Mrs Lim packs 94 cookies equally into 5 boxes. How many cookies are in each box, and how many cookies are left over?2 marks

Answer: 18 cookies in each box; 4 left overShare equally, so divide. 9 ÷ 5 = 1 r 4. Bring down 4 to make 44. 44 ÷ 5 = 8 r 4. So 94 ÷ 5 = 18 remainder 4. Each box gets 18 cookies and 4 cookies are left over.

11. 350 pupils go on a trip. Each bus can carry 8 pupils. How many buses are needed to carry all of them?2 marks

Answer: 44 buses350 ÷ 8: 3 is smaller than 8, so use the next digit too. 35 ÷ 8 = 4 r 3. Bring down 0 to make 30. 30 ÷ 8 = 3 r 6. So 350 ÷ 8 = 43 remainder 6. 43 full buses carry 344 pupils, and 6 pupils are left, so one more bus is needed. 43 + 1 = 44 buses.

12. Three ribbons of the same length are 189 cm long altogether. Mei cuts one ribbon into pieces of 7 cm each. How many pieces does she get?2 marks

Answer: 9 piecesOne ribbon: 189 ÷ 3 = 63 cm. Pieces: 63 ÷ 7 = 9. She gets 9 pieces.

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Primary 4 Mathematics · Chapter 3 · Answers and explanations

Lesson 3.5: Division of 4-Digit Numbers (answers)

Section A · Multiple choice 4 marks

1. What is 6,372 ÷ 3?1 mark

(A) 2,024(B) 2,124(C) 212(D) 2,134

Answer: (B) 2,1246 ÷ 3 = 2. Bring down 3 to make 3. 3 ÷ 3 = 1. Bring down 7 to make 7. 7 ÷ 3 = 2 r 1. Bring down 2 to make 12. 12 ÷ 3 = 4. So 6,372 ÷ 3 = 2,124.

2. Find the quotient and the remainder of 3,528 ÷ 5.1 mark

(A) Quotient 70; remainder 3(B) Quotient 706; remainder 3(C) Quotient 705; remainder 3(D) Quotient 3; remainder 705

Answer: (C) Quotient 705; remainder 33 is smaller than 5, so use the next digit too. 35 ÷ 5 = 7. Bring down 2 to make 2. 2 ÷ 5 = 0 r 2 (write 0). Bring down 8 to make 28. 28 ÷ 5 = 5 r 3. So 3,528 ÷ 5 = 705 remainder 3.

3. What is 8,056 ÷ 8?1 mark

(A) 107(B) 1,070(C) 1,700(D) 1,007

Answer: (D) 1,0078 ÷ 8 = 1. Bring down 0 to make 0. 0 ÷ 8 = 0 (write 0). Bring down 5 to make 5. 5 ÷ 8 = 0 r 5 (write 0). Bring down 6 to make 56. 56 ÷ 8 = 7. So 8,056 ÷ 8 = 1,007. The 0 in the hundreds and tens places must be kept, so the answer is 1,007.

4. Round 7,912 to the nearest thousand to estimate 7,912 ÷ 4. What is the estimate?1 mark

(A) 2,000(B) 200(C) 20,000(D) 1,000

Answer: (A) 2,0007,912 is close to 8,000. Estimate: 8,000 ÷ 4 = 2,000. (The exact answer is 1,978.)

Section B · Write your answer 11 marks

5. What is 5,418 ÷ 6?1 mark

Answer: 9035 is smaller than 6, so use the next digit too. 54 ÷ 6 = 9. Bring down 1 to make 1. 1 ÷ 6 = 0 r 1 (write 0). Bring down 8 to make 18. 18 ÷ 6 = 3. So 5,418 ÷ 6 = 903.

6. Find the quotient and the remainder of 7,205 ÷ 9.1 mark

Answer: Quotient 800; remainder 57 is smaller than 9, so use the next digit too. 72 ÷ 9 = 8. Bring down 0 to make 0. 0 ÷ 9 = 0 (write 0). Bring down 5 to make 5. 5 ÷ 9 = 0 r 5 (write 0). So 7,205 ÷ 9 = 800 remainder 5.

7. What is 2,436 ÷ 7?1 mark

Answer: 3482 is smaller than 7, so use the next digit too. 24 ÷ 7 = 3 r 3. Bring down 3 to make 33. 33 ÷ 7 = 4 r 5. Bring down 6 to make 56. 56 ÷ 7 = 8. So 2,436 ÷ 7 = 348.

8. What is 4,008 ÷ 4?1 mark

Answer: 1,0024 ÷ 4 = 1. Bring down 0 to make 0. 0 ÷ 4 = 0 (write 0). Bring down 0 to make 0. 0 ÷ 4 = 0 (write 0). Bring down 8 to make 8. 8 ÷ 4 = 2. So 4,008 ÷ 4 = 1,002. Write 0 each time the digit is too small to divide.

9. Find the quotient and the remainder of 8,125 ÷ 3.1 mark

Answer: Quotient 2,708; remainder 18 ÷ 3 = 2 r 2. Bring down 1 to make 21. 21 ÷ 3 = 7. Bring down 2 to make 2. 2 ÷ 3 = 0 r 2 (write 0). Bring down 5 to make 25. 25 ÷ 3 = 8 r 1. So 8,125 ÷ 3 = 2,708 remainder 1.

10. A store has 3,257 pencils. It packs them into packs of 6. How many full packs can it make, and how many pencils are left over?2 marks

Answer: 542 full packs; 5 pencils left overDivide by 6. 3 is smaller than 6, so use the next digit too. 32 ÷ 6 = 5 r 2. Bring down 5 to make 25. 25 ÷ 6 = 4 r 1. Bring down 7 to make 17. 17 ÷ 6 = 2 r 5. So 3,257 ÷ 6 = 542 remainder 5. So there are 542 full packs and 5 pencils left over.

11. A factory packs 7,254 bolts equally into 9 boxes. A shop buys 4 boxes. How many bolts does the shop buy?2 marks

Answer: 3,224Bolts in 1 box: 7,254 ÷ 9. 7 is smaller than 9, so use the next digit too. 72 ÷ 9 = 8. Bring down 5 to make 5. 5 ÷ 9 = 0 r 5 (write 0). Bring down 4 to make 54. 54 ÷ 9 = 6. So 1 box has 806 bolts. Bolts in 4 boxes: 806 × 4 = 3,224.

12. Mei pours 8,400 ml of juice equally into 5 bottles. She then pours the juice from 2 bottles into a jug. How much juice is in the jug?2 marks

Answer: 3,360 mlJuice in 1 bottle: 8,400 ÷ 5 = 1,680 ml (8 ÷ 5 = 1 r 3, 34 ÷ 5 = 6 r 4, 40 ÷ 5 = 8, 0 ÷ 5 = 0). Juice in 2 bottles: 1,680 × 2 = 3,360 ml.

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Primary 4 Mathematics · Chapter 3 · Answers and explanations

Lesson 3.6: Word Problems (answers)

Section A · Multiple choice 4 marks

1. Each box holds 450 sheets of paper. How many sheets are in 6 boxes?1 mark

(A) 456(B) 270(C) 2,700(D) 27,000

Answer: (C) 2,7006 equal boxes, so multiply. 450 × 6: 45 × 6 = 270, then add the zero: 2,700. There are 2,700 sheets.

2. Mei has 235 stamps. Ravi has 4 times as many stamps as Mei. How many stamps does Ravi have?1 mark

(A) 239(B) 705(C) 59(D) 940

Answer: (D) 940Ravi has 4 units and each unit is 235. 235 × 4 = 940. Ravi has 940 stamps. (Do not add: "4 times as many" means multiply.)

3. Siti has $850. Mei has $395. How much more money does Siti have than Mei?1 mark

(A) $455(B) $1,245(C) $555(D) $465

Answer: (A) $455To find how much more, subtract. $850 − $395 = $455. Siti has $455 more.

4. Ali and Ben have 120 cards altogether. Ben has 30 more cards than Ali. How many cards does Ali have?1 mark

(A) 75(B) 45(C) 90(D) 60

Answer: (B) 45Take away the 30 extra: 120 − 30 = 90. Two equal units make 90, so 1 unit = 90 ÷ 2 = 45. Ali has 45 cards. (Ben has 75.)

Section B · Write your answer 11 marks

5. Priya shares 1,848 beads equally among 6 children. How many beads does each child get?1 mark

Answer: 308 beadsEqual sharing, so divide. 1 is smaller than 6, so use the next digit too. 18 ÷ 6 = 3. Bring down 4 to make 4. 4 ÷ 6 = 0 r 4 (write 0). Bring down 8 to make 48. 48 ÷ 6 = 8. So 1,848 ÷ 6 = 308. Each child gets 308 beads.

6. Tank A has 1,350 litres of water. Tank B has 3 times as much water as Tank A. How many litres of water does Tank B have?1 mark

Answer: 4,050 litresTank B has 3 units of 1,350. 1,350 × 3 = 4,050. Tank B has 4,050 litres.

7. Class 4A recycles 2,365 kg of paper. Class 4B recycles 1,978 kg. How many kg more does Class 4A recycle than Class 4B?1 mark

Answer: 387 kgSubtract to find the difference. 2,365 − 1,978 = 387. Class 4A recycles 387 kg more.

8. Ali has 5 times as many stamps as Mei. Ali has 1,265 stamps. How many stamps does Mei have?1 mark

Answer: 253 stampsAli has 5 units, so 1 unit = 1,265 ÷ 5 = 253. Mei has 253 stamps.

9. Two ribbons are 90 cm long altogether. The long ribbon is 12 cm longer than the short ribbon. How long is the long ribbon?1 mark

Answer: 51 cmTake away the 12 cm extra: 90 − 12 = 78. Two equal units make 78, so 1 unit = 78 ÷ 2 = 39 cm. This is the short ribbon. Long ribbon: 39 + 12 = 51 cm.

10. Ravi has 5 times as many marbles as Siti. They have 1,260 marbles altogether. How many more marbles does Ravi have than Siti?2 marks

Answer: 840 marblesSiti has 1 unit and Ravi has 5 units, so there are 6 units in all. 1 unit = 1,260 ÷ 6 = 210. Ravi has 4 more units than Siti: 4 × 210 = 840 marbles.

11. Mei and Ali have $356 altogether. Ali has $48 more than Mei. How much money does Ali have?2 marks

Answer: $202Take away the $48 extra: $356 − $48 = $308. Two equal units make $308, so 1 unit = $308 ÷ 2 = $154. This is Mei's money. Ali: $154 + $48 = $202.

12. A school buys 24 boxes of markers with 12 markers in each box. 72 markers are given to Primary 3. The rest are shared equally among 8 classes. How many markers does each class get?2 marks

Answer: 27 markersTotal markers: 24 × 12 = 288 (24 × 2 = 48, 24 × 10 = 240, 48 + 240 = 288). Markers left: 288 − 72 = 216. Each class: 216 ÷ 8 = 27 (21 ÷ 8 = 2 r 5, 56 ÷ 8 = 7). Each class gets 27 markers.

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Primary 4 Mathematics · Chapter 3 · Answers and explanations

Chapter 3 Revision Paper: Four Operations of Whole Numbers (answers)

Section A · Multiple choice 10 marks

1. What is 6 × 47?1 mark

(A) 282(B) 242(C) 2,442(D) 272

Answer: (A) 2826 × 40 = 240 and 6 × 7 = 42. Add: 240 + 42 = 282. (If you forget to add the carried 4 tens, you get 242.)

2. What is 308 × 5?1 mark

(A) 1,504(B) 1,540(C) 1,040(D) 15,040

Answer: (B) 1,5408 × 5 = 40, write 0 and carry 4. 0 × 5 = 0, plus the 4 carried = 4. 3 × 5 = 15. The answer is 1,540. (Do not forget the zero in the tens.)

3. What is 2,406 × 4?1 mark

(A) 8,624(B) 9,024(C) 9,624(D) 9,424

Answer: (C) 9,6246 × 4 = 24; 0 × 4 = 0 plus 2 carried = 2; 4 × 4 = 16; 2 × 4 = 8 plus 1 carried = 9. So 2,406 × 4 = 9,624.

4. Which is the best estimate of 4,876 × 3?1 mark

(A) 12,000(B) 20,000(C) 1,500(D) 15,000

Answer: (D) 15,000Round 4,876 to the nearest thousand: 5,000. Then 5,000 × 3 = 15,000.

5. What is 23 × 40?1 mark

(A) 920(B) 92(C) 9,200(D) 690

Answer: (A) 92023 × 4 = 92, then multiply by 10 by adding a zero: 920. (92 is only 23 × 4, and 690 is 23 × 30.)

6. What is 47 × 36?1 mark

(A) 423(B) 1,692(C) 1,410(D) 1,974

Answer: (B) 1,69247 × 6 = 282. 47 × 30 = 1,410. Add the two partial products: 282 + 1,410 = 1,692.

7. What is 408 ÷ 4?1 mark

(A) 12(B) 112(C) 102(D) 1,002

Answer: (C) 1024 ÷ 4 = 1 hundred. 0 tens ÷ 4 = 0 tens (write 0). 8 ÷ 4 = 2 ones. So 408 ÷ 4 = 102. (Keep the 0 as a place holder.)

8. What is 527 ÷ 6?1 mark

(A) 78 remainder 5(B) 87(C) 8 remainder 47(D) 87 remainder 5

Answer: (D) 87 remainder 56 × 87 = 522 and 527 − 522 = 5. So 527 ÷ 6 = 87 remainder 5.

9. What is 2,412 ÷ 6?1 mark

(A) 402(B) 42(C) 412(D) 4,002

Answer: (A) 40224 hundreds ÷ 6 = 4 hundreds. 1 ten cannot be shared by 6, so write 0 in the tens. 12 ones ÷ 6 = 2 ones. So the answer is 402. Check: 402 × 6 = 2,412.

10. Ben has 3 times as many stickers as Amy. They have 1,248 stickers altogether. How many stickers does Amy have?1 mark

(A) 936(B) 312(C) 416(D) 624

Answer: (B) 312Amy has 1 unit and Ben has 3 units, so there are 4 units altogether. 1 unit = 1,248 ÷ 4 = 312. Amy has 312 stickers. (936 is Ben's.)

Section B · Short answers 4 marks

11. Find the value of 6 × 438.1 mark

Answer: 2,6286 × 400 = 2,400 and 6 × 38 = 228. Add: 2,400 + 228 = 2,628.

12. Find the value of 3,407 × 6.1 mark

Answer: 20,4427 × 6 = 42, write 2 and carry 4. 0 × 6 = 0 plus 4 = 4. 4 × 6 = 24, write 4 and carry 2. 3 × 6 = 18 plus 2 = 20. The answer is 20,442.

13. Find the value of 58 × 24.1 mark

Answer: 1,39258 × 4 = 232. 58 × 20 = 1,160. Add the partial products: 232 + 1,160 = 1,392.

14. Divide 4,567 by 8. Write the quotient and the remainder.1 mark

Answer: 570 remainder 745 hundreds ÷ 8 = 5 hundreds, 5 left. 56 tens ÷ 8 = 7 tens. 7 ones ÷ 8 = 0 ones, so write 0 and 7 is the remainder. Check: 8 × 570 = 4,560 and 4,560 + 7 = 4,567. The quotient is 570 and the remainder is 7.

Section C · Show your working 16 marks

15. Mr Tan bought 4 chairs at $135 each and a table for $218. How much did he pay altogether?2 marks

Answer: $7584 chairs: 4 × $135 = $540. Add the table: $540 + $218 = $758. He paid $758 altogether.

16. A shop bought 45 boxes of pencils. Each box has 36 pencils. The shop sold 1,500 pencils. How many pencils are left?2 marks

Answer: 120 pencilsTotal pencils: 45 × 36 = 1,620 (36 × 5 = 180, 36 × 40 = 1,440, 180 + 1,440 = 1,620). Left: 1,620 − 1,500 = 120 pencils.

17. Rina has 395 beads. She uses 6 beads to make each bracelet. How many bracelets can she make, and how many beads are left over?2 marks

Answer: 65 bracelets; 5 beads left395 ÷ 6: 39 tens ÷ 6 = 6 tens, 3 tens left. 35 ones ÷ 6 = 5 ones, 5 left. So 395 ÷ 6 = 65 remainder 5. She makes 65 bracelets with 5 beads left over.

18. A farm packs 2,184 eggs into trays. Each tray holds 8 eggs. Each tray of eggs is sold for $5. How much money is collected from selling all the trays?2 marks

Answer: $1,365Number of trays: 2,184 ÷ 8 = 273 (21 ÷ 8 = 2 r 5; 58 ÷ 8 = 7 r 2; 24 ÷ 8 = 3). Money collected: 273 × $5 = $1,365.

19. Kiran has 4 times as many cards as Lena. Together they have 1,085 cards. How many more cards does Kiran have than Lena?2 marks

Answer: 651 cardsLena has 1 unit and Kiran has 4 units, so there are 5 units altogether. 1 unit = 1,085 ÷ 5 = 217. Kiran has 4 − 1 = 3 more units than Lena: 3 × 217 = 651 cards.

20. Tank P and Tank Q hold 2,450 litres of water altogether. Tank P holds 360 litres more than Tank Q. How many litres of water does Tank P hold?2 marks

Answer: 1,405 litresTake away the extra 360 litres: 2,450 − 360 = 2,090. Two equal units make 2,090, so 1 unit = 2,090 ÷ 2 = 1,045. This is Tank Q. Tank P: 1,045 + 360 = 1,405 litres.

21. Ali, Ben and Cara have 1,350 stamps altogether. Ali has twice as many stamps as Ben. Cara has 150 more stamps than Ben. How many stamps does Cara have?2 marks

Answer: 450 stampsTake away the extra 150: 1,350 − 150 = 1,200. Now Ben has 1 unit, Ali has 2 units and Cara has 1 unit, so 4 units make 1,200. 1 unit = 1,200 ÷ 4 = 300. Cara: 300 + 150 = 450 stamps.

22. Sam saved $35 every week for 24 weeks. He used all his savings except $60 to buy a bicycle and a helmet. The bicycle cost 5 times as much as the helmet. How much did the bicycle cost? (In the model, the gold unit is the helmet and the 5 blue units are the bicycle.)2 marks

Answer: $650Savings: 24 × $35 = $840 (35 × 4 = 140, 35 × 20 = 700). Spent: $840 − $60 = $780. The helmet is 1 unit and the bicycle is 5 units, so 6 units make $780. 1 unit = $780 ÷ 6 = $130. Bicycle: 5 × $130 = $650.

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