The ratio of boys to girls is 5 to 4. There are 80 boys

If you are trying to find the ratio of boys to girls if there are 80 boys then all you do is:

1) Set up a proportion: 5/4 and 80/x

2) Cross multiply and divide:

5x = 80 (4)

5x = 320

x = 320/5

x = 64

So if the ratio of boys to girls is 5 to 4 and there are 80 boys, then there are 64 girls.