Two-digit adding and taking away · Usually met around P1
Adding three numbers
Find two that make 10 first.
How to do it
Method
Find two that make 10 first
7 + 6 + 3 = 7 + 3 + 6 = 10 + 6 = 16
Another way
Left to right
7 + 6 = 13, 13 + 3 = 16
In full
To add three numbers you can go left to right, one at a time: 7 + 6 + 3 → 7 + 6 = 13, 13 + 3 = 16. Or first find two numbers that make 10 (or a whole ten) and add those first: 7 + 3 = 10, 10 + 6 = 16. Adding can be done in any order, any two first, and the answer is the same. Two-digit numbers too: 25 + 18 + 5 → 25 + 5 = 30, then 30 + 18 = 48.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
6 + 4 + 8 = □
Show the answer and working
Answer: 18
6 and 4 make 10: add them first, then 8: 10 + 8 = 18.
Example 2
7 + 8 + 3 = 7 + 3 + □ = □ + 8 = □
Fill in each box
Show the answer and working
Answer: 8，10，18
Change the order so 7 and 3 are together: 7 + 3 = 10, 10 + 8 = 18.
Example 3
2 + 5 + 5 = 12
True or false?
Show the answer and working
Answer: True
2 + 5 + 5 = 12: find two that make 10 first, or go left to right.
Practise it in the game →Two-digit adding and taking away · Free to start, unlimited questions, no download