There were 110 children enrolled in the Hazel Swimming School in 2016. ⁵₁₁ of the children were boys. Additional children joined the swimming school in 2017. For every 5 boys who joined the swimming school, 4 girls joined the swimming school. If there was an equal number of girls and boys in 2017, how many girls joined the school in that year?

	Boys	Girls
Before	50	60
Change	+ 5 u	+ 4 u
After	50 + 5 u	60 + 4 u

Fraction of children who are girls
= 1 - ⁵₁₁
= ⁶₁₁

Number of boys at first
= ⁵₁₁ x 110
= 50

Number of girls at first
= ⁶₁₁ x 110
= 60

Boys who joined : Girls who joined
5 : 4

The number of girls and boys in the end is the same.

50 + 5 u = 60 + 4 u
5 u - 4 u = 60 - 50

1 u = 10

Number of girls who joined the school in that year
= 4 u
= 4 x 10
= 40

Answer(s): 40