The r% of a quantity x is computed by dividing x in 100 parts, and considering r of such parts. So, the r% of the male is
and similarly, the r% of female is
The number of males decreased by this quantity, so now it is
and the number of female increased by this quantity, so now it is
we know that these two new counts are the same number, so we can build and solve the equality
Subtract 20 and add 0.3r from both sides:
Divide both sides by 0.5 to solve for r:
Let's check the answer
The 20% of 30 is , while the 20% of 20 is 4. So, we are stating that
which is true because both expressions evaluate to 24.