PSLE
In a school, 30% of the members in Computer Club and 75% of the members in Art Club are girls. Both clubs have the same number of boys. The Art Club has 54 more girls than the Computer Club. How many girls are there altogether?

	Computer Club		Art Club
Types	Girls	Boys	Girls	Boys
Comparing the girls and the boys in each club	3x1	7x1	3x7	1x7
Comparing the boys in 2 clubs		1		1
	3 u	7 u	21 u	7 u

30% = ³⁰₁₀₀ = ³₁₀

Fraction of the members in Computer Club that are boys
= 1 - ³₁₀
= ⁷₁₀

75% = ⁷⁵₁₀₀ = ³₄

Fraction of the members in Art club that are boys
= 1 - ³₄
= ¹₄

The number of boys in both clubs is the same. Make the numerators the same. LCM of 7 and 1 is 7. 

7x110x1 of the members in Computer Club = 1x74x7 of the members in Art Club
710of the members in Computer Club = 728 of the members in Art Club

Number of more girls in Art Club than Computer Club
= 21 u - 3 u
= 18 u

18 u = 54

1 u = 54 ÷ 18 = 3

Total number of girls
= 3 u + 21 u
= 24 u
= 24 x 3
= 72

Answer(s): 72