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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