Okay, so the ratio is 5:4. Meaning that the guys represent the number 5 and girls represent the number 4. If there are 40 boys, and 5 times 8 is 40, you also need to multiply 4 and 8 together to figure out how many girls there are in the club. So 4 times 8 is 32. So when you add 40 (guys) and 32 (girls) you get 72 total members.
