Decimals · Usually met around P4
Three decimals added and taken away
Line up the points; left to right.
How to do it
Method
Line up the points; left to right
2.37 + 4.5 + 0.63 = 3 + 4.5 = 7.5
Another way
Add the two, take away once
9.6 − 2.3 − 1.7 = 9.6 − 4 = 5.6
In full
To add and take away decimals, line up the points: ones under ones, tenths under tenths. A whole number's point sits after its ones: 3.25 + 4 = 7.25. With adding and taking away together, work left to right: 10 − 3.45 + 1.2 = 6.55 + 1.2 = 7.75. With only adding, first add the two that make a whole number: 2.37 + 4.5 + 0.63 = (2.37 + 0.63) + 4.5 = 3 + 4.5 = 7.5. Taking away two numbers in a row, you may add them first and take away once: 9.6 − 2.3 − 1.7 = 9.6 − 4 = 5.6. Or work step by step in columns: the same answer.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
9.1 + 1.7 + 9.2 = □
Show the answer and working
Answer: 20
Line up the points and add them one at a time, left to right.
Example 2
6.06 + 5.4 + 6.94 = □
Show the answer and working
Answer: 18.4
First add 6.06 and 6.94, which make a whole number, 13; then add 5.4.
Example 3
What is 1.33 + 2 + 1.2?
- A. 2.73
- B. 2.55
- C. 3.45
- D. 4.53
Choose the right answer
Show the answer and working
Answer: D. 4.53
Line up the points: 1.33 + 2 + 1.2 = 4.53.
Practise it in the game →Decimals · Free to start, unlimited questions, no download