Answer:
There are 12 boys at the movie.
Explanation:
Key skills needed in order to solve: Proportions, Ratios, and Multiplication
1) The ratio is 4 boys : 5 girls --> It can be written as a fraction --> 4/5
2) If there are 15 girls, we need to find the number of boys. let's say x is the number of boys when there are 15 girls. The ratio would then be x/15
3) Make a proportion -->
=
You have to cross multiply here. You do the first fraction's numerator times the second fraction's denominator, and the first fraction's denominator times the second fraction's numerator.
4) This means you have to do: 4(15) = 5(x)
5) Multiply it out --> 60=5x
6) Divide by 5 and you will get x=12
Therefore there are 12 boys at the movie.
Hope you understand and have a nice day!! :D