21 is what percent of 42

21 is 50% of 42.

42 x 0.5 = 21

1. We assume, that the number 42 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 100% equals 42, so we can write it down as 100%=42.

4. We know, that x% equals 21 of the output value, so we can write it down as x%=21.

5. Now we have two simple equations:

1) 100%=42

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:

100%/x%=42/21

6. Now we just have to solve the simple equation, and we will get the solution we are looking for.

7. Solution for 21 is what percent of 42

100%/x%=42/21

(100/x) * x = (42/21) * x - we multiply both sides of the equation by x

100=2*x - we divide both sides of the equation by (2) to get x

100/2=x

50=x

x=50

now we have:

21 is 50% of 42