Answer: 25 girls are in the class
Step-by-step explanation: You can set up the ratio 4:5 as a fraction,
to find your answer. You are given the fact that 20 boys are in the class so now you can solve 2 ways.
Option 1 - Set up the equation algebraically as
, where x = number of girls and set that equal to
. This way allows you to see that the fraction must have the same ratio as 4:5. You can see that 4 x 5 = 20, so the multiple factor is 5. The variable x must equal 5 x 5, so x = 25.
Option 2 - Multiply the amount of boys given to you by the reciprocal of the ratio. Instead of using
, you have to use
because there are more girls than boys in the class. This allows you to finish the problem by multiplying 20 x
to get the result of
, which you may know simplifies into 25.