Primary 4 Mathematics · Chapter 10 · Answers and explanations

Lesson 10.4: Multiplication of Decimals (answers)

Section A · Multiple choice 4 marks

1. 0.4 × 3 = ?1 mark

(A) 12(B) 1.2(C) 0.12(D) 7

Answer: (B) 1.24 tenths × 3 = 12 tenths = 1.2.

2. 2.3 × 4 = ?1 mark

(A) 8.12(B) 8.2(C) 9.2(D) 92

Answer: (C) 9.23 tenths × 4 = 12 tenths: write 2, carry 1. 2 × 4 = 8, plus 1 = 9. So 9.2.

3. 3.06 × 5 = ?1 mark

(A) 15.03(B) 1.53(C) 153(D) 15.3

Answer: (D) 15.36 hundredths × 5 = 30 hundredths: write 0, carry 3 tenths. 0 × 5 + 3 = 3 tenths. 3 × 5 = 15. So 15.30 = 15.3.

4. 4.28 × 3 = ?1 mark

(A) 12.84(B) 12.24(C) 13.84(D) 128.4

Answer: (A) 12.848 × 3 = 24: write 4, carry 2. 2 × 3 = 6, plus 2 = 8. 4 × 3 = 12. So 12.84.

5. 0.05 × 8 = ______1 mark

Answer: 0.45 hundredths × 8 = 40 hundredths = 0.40 = 0.4.

6. 0.7 × 6 = ______1 mark

Answer: 4.27 tenths × 6 = 42 tenths = 4.2.

7. 5.4 × 3 = ______1 mark

Answer: 16.24 × 3 = 12: write 2, carry 1. 5 × 3 = 15, plus 1 = 16. So 16.2.

8. 6.25 × 4 = ______1 mark

Answer: 255 × 4 = 20: write 0, carry 2. 2 × 4 = 8, plus 2 = 10: write 0, carry 1. 6 × 4 = 24, plus 1 = 25. So 25.00 = 25.

9. 12.6 × 5 = ______1 mark

Answer: 636 × 5 = 30: write 0, carry 3. 2 × 5 = 10, plus 3 = 13: write 3, carry 1. 1 × 5 = 5, plus 1 = 6. So 63.0 = 63.

10. 3.48 × 9 = ______2 marks

Answer: 31.328 × 9 = 72: write 2, carry 7. 4 × 9 = 36, plus 7 = 43: write 3, carry 4. 3 × 9 = 27, plus 4 = 31. So 31.32.

11. 45.07 × 6 = ______2 marks

Answer: 270.427 × 6 = 42, write 2 carry 4. 0 × 6 + 4 = 4. 5 × 6 = 30, write 0 carry 3. 4 × 6 = 24, plus 3 = 27. So 270.42.

12. Each pack of cards costs $4.85. How much do 6 packs cost?2 marks

Answer: $29.104.85 × 6 = 29.10. The cost is $29.10.

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