Three-digit adding and taking away · Usually met around P2
Adding and taking away together
With + and −, go left to right.
How to do it
Method
With + and −, go left to right
72 − 25 + 18 = 47 + 18 = 65
Another way
Add first, then take away
72 + 18 = 90, 90 − 25 = 65
In full
When a line has both + and −, work from left to right: 72 − 25 + 18, first 72 − 25 = 47, then 47 + 18 = 65. Don't do 25 + 18 first: that gives 72 − 43 = 29, which is wrong. Think of a bus: 72 on board, 25 get off, then 18 get on. Or check by adding first and taking away after: 72 + 18 = 90, 90 − 25 = 65, the same.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
Work out 339 + 125 − 131: first 339 + 125 = □, then take away 131 to get □.
Fill in each box
Show the answer and working
Answer: 464，333
339 + 125 = 464; 464 − 131 = 333.
Example 2
617 − 95 + 81 = 617 − 14
True or false?
Show the answer and working
Answer: True
Taking away 95 and adding back 81 takes away only 95 − 81 in all; left to right, the answer is 603.
Example 3
415 + □ − 111 = 416
Show the answer and working
Answer: 112
Work backwards: before taking away 111 it was 416 + 111 = 527, and 527 − 415 = 112.
Practise it in the game →Three-digit adding and taking away · Free to start, unlimited questions, no download