Answer:
10 girls
Explanation:
We can show our ratio as a fraction:

Since the denominator of 5 is the total number of participants and the numberator is the # of girls in the competition, we can write another proportional ratio.
It would be:

and
would be proportional. To solve this, we can find a number that can be multiplied, by both the numerator and the denominator, which gives a value of 25 for the denominator.
This number would be 5.
If we multiply the denomitator of
by 5, we get 25, which is the value of the other fraction. Now, if we multiply the numerator by 5, we get 10, which is the number of girls in the competition.