Adding and subtracting decimals worksheet

Part A: Working out and filling in

1. 1. 0.78 − 0.58 = 0.2

   0.78 − 0.58: both have two places, so work as whole numbers, 78 − 58 = 20, then put the point back two places → 0.20 = 0.2

2. 2. 0.8 − 0.14 = 0.66

   0.8 − 0.14: write 0.8 as 0.80, both have two places, so work as whole numbers, 80 − 14 = 66, then put the point back two places → 0.66

3. 3. 9.9 + 2.8 = 12.7

   9.9 + 2.8: both have one place, so work as whole numbers, 99 + 28 = 127, then put the point back one place → 12.7

4. 4. 9.2 + 7.1 = 16.3

   9.2 + 7.1: both have one place, so work as whole numbers, 92 + 71 = 163, then put the point back one place → 16.3

5. 5. 0.69 + 0.8 = 1.49

   0.69 + 0.8: write 0.8 as 0.80, both have two places, so work as whole numbers, 69 + 80 = 149, then put the point back two places → 1.49

6. 6. 9.7 + 5.7 = 15.4

   9.7 + 5.7: both have one place, so work as whole numbers, 97 + 57 = 154, then put the point back one place → 15.4

7. 7. 5.9 + 9.4 = 15.3

   5.9 + 9.4: both have one place, so work as whole numbers, 59 + 94 = 153, then put the point back one place → 15.3

8. 8. 9.2 − 4.7 = 4.5

   9.2 − 4.7: both have one place, so work as whole numbers, 92 − 47 = 45, then put the point back one place → 4.5

9. 9. 7.2 − 5.3 = 1.9

   7.2 − 5.3: both have one place, so work as whole numbers, 72 − 53 = 19, then put the point back one place → 1.9

10. 10. 5.5 − 5.2 = 0.3

    5.5 − 5.2: both have one place, so work as whole numbers, 55 − 52 = 3, then put the point back one place → 0.3

11. 11. 9.4 − 6.5 = 2.9

    9.4 − 6.5: both have one place, so work as whole numbers, 94 − 65 = 29, then put the point back one place → 2.9

12. 12. 7.8 + 7.1 = 14.9

    7.8 + 7.1: both have one place, so work as whole numbers, 78 + 71 = 149, then put the point back one place → 14.9

Part B: Word problems

Marking: 2 for the working, 1 for the answer, 1 for the sentence.

1. 13. In the long jump, Ka-yan jumped 3.32 m and Chi-keung jumped 1.9 m. How many metres further did Ka-yan jump than Chi-keung? (Answer: 1.42 m)

   3.32 − 1.9 = 1.42

2. 14. In the long jump, Tsz-ching jumped 3.28 m and Ka-yee jumped 2.11 m. How many metres further did Tsz-ching jump than Ka-yee? (Answer: 1.17 m)

   3.28 − 2.11 = 1.17

3. 15. Ka-yan buys a pen for $4.2 and a notebook for $15.9, and pays with a $50 note. How much change should she get, in dollars? (Answer: 29.9 dollars)

   4.2 + 15.9 = 20.1; 50 − (4.2 + 15.9) = 29.9

4. 16. May buys a pen for $3.4 and a notebook for $8.3, and pays with a $50 note. How much change should she get, in dollars? (Answer: 38.3 dollars)

   3.4 + 8.3 = 11.7; 50 − (3.4 + 8.3) = 38.3

5. 17. Chi-keung buys a pen for $7.6 and a notebook for $16.8. How many dollars must he pay altogether? (Answer: 24.4 dollars)

   7.6 + 16.8 = 24.4

6. 18. Monday's rainfall was 2.7 mm, and Tuesday's was 3.9 mm more than Monday's. What was the total rainfall over the two days, in millimetres? (Answer: 9.3 mm)

   2.7 + 3.9 = 6.6; 2.7 + (2.7 + 3.9) = 9.3