81 is what percent of 639 - 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 639 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 639, so we can write it down as 100%=639.
4. We know, that x% equals 81 of the output value, so we can write it down as x%=81.
5. Now we have two simple equations:
1) 100%=639
2) x%=81
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%=639/81
6. Now we just have to solve the simple equation, and we will get the solution we are looking for.

7. Solution for 81 is what percent of 639

100%/x%=639/81
(100/x)*x=(639/81)*x       - we multiply both sides of the equation by x
100=7.8888888888889*x       - we divide both sides of the equation by (7.8888888888889) to get x
100/7.8888888888889=x
12.676056338028=x
x=12.676056338028

now we have:
81 is 12.676056338028% of 639