What is 20 percent of 640.09 - 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 640.09 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 640.09 is 100%, so we can write it down as 640.09=100%.
4. We know, that x is 20% of the output value, so we can write it down as x=20%.
5. Now we have two simple equations:
1) 640.09=100%
2) x=20%
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:
640.09/x=100%/20%
6. Now we just have to solve the simple equation, and we will get the solution we are looking for.

7. Solution for what is 20% of 640.09

640.09/x=100/20
(640.09/x)*x=(100/20)*x       - we multiply both sides of the equation by x
640.09=5*x       - we divide both sides of the equation by (5) to get x
640.09/5=x
128.018=x
x=128.018

now we have:
20% of 640.09=128.018