To write a fraction as a percent, first remember that a percent is a ratio of a number to 100. If we want to write 
 as a percent, we need to find a fraction equivalent to
 as a percent, we need to find a fraction equivalent to 
 that has a 100 in the denominator. We can do this by setting up a proportion.
 that has a 100 in the denominator. We can do this by setting up a proportion.
 
 =
 = 

Now, we can use cross products to find the missing value.
20n = 900
÷20 ÷20 ← divide by 20 on both sides
n = 45
Therefore, 
 is equal to
 is equal to 
 or 45%.
 or 45%.