Step by step
The question
Question: work out 26 + 58 + 4 in your head.
26 + 58 + 4
1 Find the easy pair
Look for two numbers that make a round number.
26 plus 4 is 30.
That is easy.
2 Change the order
We move 4 next to 26.
= 26 + 4 + 58
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.
= (26 + 4) + 58
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
26 plus 4 is 30.
= 30 + 58
30 plus 58 is 88.
= 88
5 Check
Let's check the long way, from left to right: 26 plus 58 is 84.
84 plus 4 is 88.
The same.
So the answer is right!
26 + 58 = 84, 84 + 4 = 88
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
= 88