PSLE
In a school, 70% of the members in Reading Club and 75% of the members in Computer Club are girls. Both clubs have the same number of boys. The Reading Club has 4 less girls than the Computer Club. How many members are there in Computer Club?

	Reading Club		Computer Club
Types	Girls	Boys	Girls	Boys
Comparing the girls and the boys in each club	7x1	3x1	3x3	1x3
Comparing the boys in 2 clubs		1		1
	7 u	3 u	9 u	3 u

70% = ⁷⁰₁₀₀ = ⁷₁₀

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

75% = ⁷⁵₁₀₀ = ³₄

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

The number of boys in both clubs is the same. Make the numerators the same. LCM of 3 and 1 is 3. 

3x110x1 of the members in Reading Club = 1x34x3 of the members in Computer Club
310of the members in Reading Club = 312 of the members in Computer Club

Number of less girls in Reading Club than Computer Club
= 9 u - 7 u
= 2 u

2 u = 4

1 u = 4 ÷ 2 = 2

Number of members in Computer Club
= 12 u
= 12 x 2
= 24

Answer(s): 24