Step by step
The question
Question: find the length l of a rectangle with area 42 square units and width 6.
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 42 and the width is 6.
So l × 6 = 42.
Careful!
The area is times, not plus.
So we divide by 6.
We do not take it away.
l × 6 is the same as 6 × l: times works in any order.
3 Remove the × 6
We want l by itself.
The times 6 is in the way.
To remove times 6, we divide by 6.
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.
6 divided by 6 is 1.
So just l is left.
42 divided by 6 is 7.
So the length is 7.
4 Check
Let's check: length times width, 7 times 6.
We get 42, the area.
So the length is right!
Let's look back.
First: write the rule.
Then: put the numbers in.
Then: remove the × 6.
Last: check.