Step by step
The question
Question: find the diameter d of a circle with circumference 31.4.
1 Write the rule
The circumference is π times the diameter: C = π × d.
π is a special number for circles.
It is about 3.14.
Now put the numbers in: C = 31.4 and 3.14 for π.
Careful!
Dividing by 2 times 3.14 gives the radius.
The diameter is π times d, so we divide by 3.14 only.
2 Remove the × 3.14
We want d by itself.
The times 3.14 is in the way.
To remove times 3.14, we divide by 3.14.
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.
3.14 divided by 3.14 is 1.
So just d is left.
Check the division: 3.14 times 10 is 31.4.
31.4 divided by 3.14 is 10.
So the diameter is 10.
3 Check
Let's check: put d = 10 back in the rule.
We get 31.4 again.
So the diameter is right!
Let's look back.
First: write the rule.
Then: remove the × 3.14.
Last: check.