Three decimals added and subtracted worksheet

Part A: Working out and filling in

1. 1. 16

   Work left to right: 23.3 − 5.4 first.

   Subtract left to right; or add 5.4 and 1.9 first and subtract once.

2. 2. 16

   All three have one decimal place. Line up the points and work out 8.2 + 2.7 first.

   Line up the points and add them one at a time, left to right: 8.2 + 2.7 = 10.9, 10.9 + 5.1 = 16.

3. 3. 1.3

   Work left to right: 10.2 − 6.5 first.

   Subtract left to right; or add 6.5 and 2.4 first and subtract once.

4. 4. 14.76

   Write 17 as 17.00, line up the points and work out 17 − 4.84 first.

   Write 17 as 17.00, line up the points and go left to right: subtract 4.84, then add 2.6.

5. 5. 9.6

   Look for the two numbers whose decimal parts make a whole number, and add those first.

   First add 4.83 and 3.17, which make a whole number, 8; then add 1.6.

6. 6. 8.02

   Write 8 as 8.00, line up the points and work out 8 − 3.68 first.

   Write 8 as 8.00, line up the points and go left to right: subtract 3.68, then add 3.7.

7. 7. 10.3

   Look for the two numbers whose decimal parts make a whole number, and add those first.

   First add 7.01 and 0.99, which make a whole number, 8; then add 2.3.

8. 8. 4.6

   Work backwards: add 0.62 back on to 5.92 and you get 1.94 + □.

   Work backwards: □ = 5.92 + 0.62 − 1.94 = 4.6.

9. 9. 8.2

   Work backwards: add 0.68 back on to 12.16 and you get 4.64 + □.

   Work backwards: □ = 12.16 + 0.68 − 4.64 = 8.2.

Part B: Choose, or true or false

1. 10. C. 7.55

   3 is a whole number, so its point sits after the ones. Line up the points and work out 2.35 + 3 first.

   Line up the points: 2.35 + 3 + 2.2 = 7.55.

2. 11. True

   With adding and subtracting, go left to right: 5.14 − 1.32 first, then check whether the next step adds or subtracts.

   Left to right: 5.14 − 1.32 first, then add 2.2: 6.02.

3. 12. A. 10.02

   2 is a whole number, so its point sits after the ones. Line up the points and work out 6.92 + 2 first.

   Line up the points: 6.92 + 2 + 1.1 = 10.02.

Part C: Word problems

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

1. 13. 97.2 L

   Used means subtract, poured in means add. Left to right: 80.5 − 1.6 first.

   Used means subtract, poured in means add, left to right: 80.5 − 1.6 = 78.9, 78.9 + 18.3 = 97.2 L.

2. 14. 61.25 dollars

   The change is $100 less the two prices. You could work out 29.3 + 9.45 first.

   100 − 29.3 − 9.45: or add 29.3 and 9.45 first and take that from 100.

3. 15. 0.49 m

   Write 11 as 11.00, line up the points and subtract 3.21 first.

   Write 11 as 11.00, line up the points and subtract twice: 11 − 3.21 = 7.79, 7.79 − 7.3 = 0.49 m.

4. 16. 3.37 m

   Write 14 as 14.00, line up the points and subtract 2.73 first.

   Write 14 as 14.00, line up the points and subtract twice: 14 − 2.73 = 11.27, 11.27 − 7.9 = 3.37 m.

5. 17. 48.75 dollars

   The change is $100 less the two prices. You could work out 29.55 + 21.7 first.

   100 − 29.55 − 21.7: or add 29.55 and 21.7 first and take that from 100.

6. 18. 67.4 L

   Used means subtract, poured in means add. Left to right: 62.2 − 5.3 first.

   Used means subtract, poured in means add, left to right: 62.2 − 5.3 = 56.9, 56.9 + 10.5 = 67.4 L.