Step by step
The question
Question: work out 37 + 48 + 63 in your head.
37 + 48 + 63
1 Find the easy pair
Look for two numbers that make a round number.
37 plus 63 is 100.
That is easy.
2 Change the order
We move 63 next to 37.
= 37 + 63 + 48
In adding, the order does not matter.
This is the commutative property.
a + b = b + a
commutative: the order does not matter
3 Group the easy pair
We put brackets round the easy pair, so we do it first.
= (37 + 63) + 48
With only adding, we can group the numbers any way we like.
This is the associative property.
(a + b) + c = a + (b + c)
associative: brackets can move
Careful!
This works for adding only.
With minus or divide, the order matters.
Careful: only with +: not with − or ÷
4 Work it out
37 plus 63 is 100.
= 100 + 48
100 plus 48 is 148.
= 148
5 Check
Let's check the long way, from left to right: 37 plus 48 is 85.
85 plus 63 is 148.
The same.
So the answer is right!
37 + 48 = 85, 85 + 63 = 148
Let's look back.
First: find the easy pair.
Then: change the order.
Then: group the easy pair.
Then: work it out.
Last: check.
Answer
= 148