640.5 is what percent of 815 - 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 815 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 815, so we can write it down as 100%=815.
4. We know, that x% equals 640.5 of the output value, so we can write it down as x%=640.5.
5. Now we have two simple equations:
1) 100%=815
2) x%=640.5
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%=815/640.5
6. Now we just have to solve the simple equation, and we will get the solution we are looking for.

7. Solution for 640.5 is what percent of 815

100%/x%=815/640.5
(100/x)*x=(815/640.5)*x       - we multiply both sides of the equation by x
100=1.2724434035909*x       - we divide both sides of the equation by (1.2724434035909) to get x
100/1.2724434035909=x
78.588957055215=x
x=78.588957055215

now we have:
640.5 is 78.588957055215% of 815