There are 12 boys 10 girls in your gym class. if 6 boys joined the class, how many girls would need to join for the ratio of boys to girls to remain the same?

Answer 1

The starting ratio here is 12:10. Simplifying this (by dividing both numbers by 2) gives us 6:5.

By adding 6 boys, we're now at 18:10, and simplifying gives us 9:5, which is not what we need. Our ration must stay at 6:5

To find the number of girls needed, we first must find if we can simply 18 down to 6, by division. We can do that, since 18/6 gives us 3.

Next, we take that 3 and multiply it to the simplified girl ratio number, which was 5. This will give us 15.

And put that into our newest ratio to accommodate the new boys, we get a ratio of 18:15, and simplifying this (by dividing by 3) gives us our starting ratio of 6:5.

Since we need 15 girls to satisfy the ratio, we finally take 15 minus our starting number of girls to find out how many girls must join: 15-10 = 5 girls are needed to join to keep the ration the same.