There were 209 children enrolled in the Ivory Computer School in 2020. ⁴₁₁ of the children were girls. Additional children joined the computer school in 2021. For every 4 girls who joined the computer school, 3 boys joined the computer school. If there was an equal number of boys and girls in 2021, how many boys joined the school in that year?

	Girls	Boys
Before	76	133
Change	+ 4 u	+ 3 u
After	76 + 4 u	133 + 3 u

Fraction of children who are boys
= 1 - ⁴₁₁
= ⁷₁₁

Number of girls at first
= ⁴₁₁ x 209
= 76

Number of boys at first
= ⁷₁₁ x 209
= 133

Girls who joined : Boys who joined
4 : 3

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

76 + 4 u = 133 + 3 u
4 u - 3 u = 133 - 76

1 u = 57

Number of boys who joined the school in that year
= 3 u
= 3 x 57
= 171

Answer(s): 171