Step by step
The question
Question: find the width w of a rectangle with area 22.5 square units and length 5.
1 Write the rule
The area of a rectangle is length times width.
So A = length × width.
2 Put the numbers in
The area is 22.5 and the length is 5.
So 5 × w = 22.5.
Careful!
The area is times, not plus.
So we divide by 5.
We do not take it away.
3 Remove the × 5
We want w by itself.
The times 5 is in the way.
To remove times 5, we divide by 5.
We do it on both sides.
Why both sides?
The = sign means both sides are the same amount.
If we change only one side, they are not the same any more.
5 divided by 5 is 1.
So just w is left.
Check the division: 5 times 4.5 is 22.5.
22.5 divided by 5 is 4.5.
So the width is 4.5.
4 Check
Let's check: length times width, 5 times 4.5.
We get 22.5, the area.
So the width is right!
Let's look back.
First: write the rule.
Then: put the numbers in.
Then: remove the × 5.
Last: check.