What is 90 percent of 21.09 - 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 21.09 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 21.09 is 100%, so we can write it down as 21.09=100%.
4. We know, that x is 90% of the output value, so we can write it down as x=90%.
5. Now we have two simple equations:
1) 21.09=100%
2) x=90%
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:
21.09/x=100%/90%
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 90% of 21.09

21.09/x=100/90
(21.09/x)*x=(100/90)*x       - we multiply both sides of the equation by x
21.09=1.1111111111111*x       - we divide both sides of the equation by (1.1111111111111) to get x
21.09/1.1111111111111=x
18.981=x
x=18.981

now we have:
90% of 21.09=18.981