What is 3900 percent of 21 - 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 21 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 21 is 100%, so we can write it down as 21=100%.
4. We know, that x is 3900% of the output value, so we can write it down as x=3900%.
5. Now we have two simple equations:
1) 21=100%
2) x=3900%
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:
21/x=100%/3900%
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 3900% of 21

21/x=100/3900
(21/x)*x=(100/3900)*x       - we multiply both sides of the equation by x
21=0.025641025641026*x       - we divide both sides of the equation by (0.025641025641026) to get x
21/0.025641025641026=x
819=x
x=819

now we have:
3900% of 21=819