PSLE
In a school, 60% of the members in Reading Club and 90% of the members in Computer Club are boys. Both clubs have the same number of girls. The Reading Club has 30 less boys than the Computer Club. How many members are there in Computer Club?

	Reading Club		Computer Club
Types	Boys	Girls	Boys	Girls
Comparing the boys and the girls in each club	3x1	2x1	9x2	1x2
Comparing the girls in 2 clubs		1		1
	3 u	2 u	18 u	2 u

60% = ⁶⁰₁₀₀ = ³₅

Fraction of the members in Reading Club that are girls
= 1 - ³₅
= ²₅

90% = ⁹⁰₁₀₀ = ⁹₁₀

Fraction of the members in Computer club that are girls
= 1 - ⁹₁₀
= ¹₁₀

The number of girls in both clubs is the same. Make the numerators the same. LCM of 2 and 1 is 2. 

2x15x1 of the members in Reading Club = 1x210x2 of the members in Computer Club
25of the members in Reading Club = 220 of the members in Computer Club

Number of less boys in Reading Club than Computer Club
= 18 u - 3 u
= 15 u

15 u = 30

1 u = 30 ÷ 15 = 2

Number of members in Computer Club
= 20 u
= 20 x 2
= 40

Answer(s): 40