Primary 4 Mathematics · Chapter 10 · Answers and explanations
Lesson 10.1: Addition of Decimals (answers)
Section A · Multiple choice 4 marks
1. 3.4 + 5.3 = ?1 mark
(A) 8.07(B) 2.1(C) 8.7(D) 87
Answer: (C) 8.7Add the tenths: 4 + 3 = 7. Add the ones: 3 + 5 = 8. So 3.4 + 5.3 = 8.7.
2. 4.26 + 3.51 = ?1 mark
(A) 7.67(B) 8.77(C) 0.777(D) 7.77
Answer: (D) 7.77Hundredths: 6 + 1 = 7. Tenths: 2 + 5 = 7. Ones: 4 + 3 = 7. So 7.77.
3. 7.6 + 2.8 = ?1 mark
(A) 10.4(B) 9.14(C) 10.14(D) 9.4
Answer: (A) 10.46 tenths + 8 tenths = 14 tenths, write 4 and carry 1. 7 + 2 + 1 = 10. So 10.4.
4. 2.9 + 4.75 = ?1 mark
(A) 7.15(B) 7.65(C) 6.65(D) 7.4
Answer: (B) 7.65Write 2.9 as 2.90. Hundredths: 0 + 5 = 5. Tenths: 9 + 7 = 16, write 6 and carry 1. Ones: 2 + 4 + 1 = 7. So 7.65.
Section B · Write your answer 11 marks
5. 2.7 + 6.2 = ______1 mark
Answer: 8.9Tenths: 7 + 2 = 9. Ones: 2 + 6 = 8. So 8.9.
6. 5.08 + 3.41 = ______1 mark
Answer: 8.49Hundredths: 8 + 1 = 9. Tenths: 0 + 4 = 4. Ones: 5 + 3 = 8. So 8.49.
7. 4.9 + 3.6 = ______1 mark
Answer: 8.59 tenths + 6 tenths = 15 tenths, write 5 and carry 1. 4 + 3 + 1 = 8. So 8.5.
8. 3.67 + 2.85 = ______1 mark
Answer: 6.52Hundredths: 7 + 5 = 12, write 2 carry 1. Tenths: 6 + 8 + 1 = 15, write 5 carry 1. Ones: 3 + 2 + 1 = 6. So 6.52.
9. 15.8 + 4.35 = ______2 marks
Answer: 20.15Write 15.8 as 15.80. Then 15.80 + 4.35 = 20.15.
10. 9.48 + 0.52 = ______1 mark
Answer: 10Hundredths: 8 + 2 = 10, carry 1. Tenths: 4 + 5 + 1 = 10, carry 1. Ones: 9 + 0 + 1 = 10. So 10.00 = 10.
11. 36.4 + 7.89 = ______2 marks
Answer: 44.29Write 36.4 as 36.40. Then 36.40 + 7.89 = 44.29.
12. A rope is 12.35 m long. Another rope is 8.9 m long. What is the total length of the two ropes?2 marks
Answer: 21.25 mAdd: 12.35 + 8.90 = 21.25. The total length is 21.25 m.
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