18 is what percent of 90 - step by step solution

To get the solution, we are looking for, we need to point out what we know.

1. We assume, that the number 90 is 100% - because it's the output value of the task.
2. We assume, that x is the value we are looking for.
3. If 100% equals 90, so we can write it down as 100%=90.
4. We know, that x% equals 18 of the output value, so we can write it down as x%=18.
5. Now we have two simple equations:
1) 100%=90
2) x%=18
where left sides of both of them have the same units, and both right sides have the same units, so we can do something like that:
100%/x%=90/18
6. Now we just have to solve the simple equation, and we will get the solution we are looking for.

7. Solution for 18 is what percent of 90

100%/x%=90/18
(100/x)*x=(90/18)*x       - we multiply both sides of the equation by x
100=5*x       - we divide both sides of the equation by (5) to get x
100/5=x
20=x
x=20

now we have:
18 is 20% of 90