What is 20 percent of 640 - 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 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 is 100%, so we can write it down as 640=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=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/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

640/x=100/20
(640/x)*x=(100/20)*x       - we multiply both sides of the equation by x
640=5*x       - we divide both sides of the equation by (5) to get x
640/5=x
128=x
x=128

now we have:
20% of 640=128