What is 21 percent of 39.9 - 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 39.9 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 39.9 is 100%, so we can write it down as 39.9=100%.
4. We know, that x is 21% of the output value, so we can write it down as x=21%.
5. Now we have two simple equations:
1) 39.9=100%
2) x=21%
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:
39.9/x=100%/21%
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 21% of 39.9

39.9/x=100/21
(39.9/x)*x=(100/21)*x       - we multiply both sides of the equation by x
39.9=4.7619047619048*x       - we divide both sides of the equation by (4.7619047619048) to get x
39.9/4.7619047619048=x
8.379=x
x=8.379

now we have:
21% of 39.9=8.379