There were 275 children enrolled in the Mary Acting School in 2020. ⁵₁₁ of the children were boys. Additional children joined the acting school in 2021. For every 5 boys who joined the acting school, 4 girls joined the acting school. If there was an equal number of girls and boys in 2021, how many girls joined the school in that year?

	Boys	Girls
Before	125	150
Change	+ 5 u	+ 4 u
After	125 + 5 u	150 + 4 u

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

Number of boys at first
= ⁵₁₁ x 275
= 125

Number of girls at first
= ⁶₁₁ x 275
= 150

Boys who joined : Girls who joined
5 : 4

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

125 + 5 u = 150 + 4 u
5 u - 4 u = 150 - 125

1 u = 25

Number of girls who joined the school in that year
= 4 u
= 4 x 25
= 100

Answer(s): 100