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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

3123123123121,248
(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

Total$135$135$135$135$218$758
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

Lena217Kiran217217217217651
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

1,0451,0453602,450
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

Ben300Ali300300Cara300150
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

Cost$130$130$130$130$130$130$780$650
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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