PSLE
In a school, 60% of the members in Literary Club and 75% of the members in Chess Club are girls. Both clubs have the same number of boys. The Literary Club has 21 less girls than the Chess Club. How many members are there in Chess Club?

	Literary Club		Chess Club
Types	Girls	Boys	Girls	Boys
Comparing the girls and the boys in each club	3x1	2x1	3x2	1x2
Comparing the boys in 2 clubs		1		1
	3 u	2 u	6 u	2 u

60% = ⁶⁰₁₀₀ = ³₅

Fraction of the members in Literary Club that are boys
= 1 - ³₅
= ²₅

75% = ⁷⁵₁₀₀ = ³₄

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

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

2x15x1 of the members in Literary Club = 1x24x2 of the members in Chess Club
25of the members in Literary Club = 28 of the members in Chess Club

Number of less girls in Literary Club than Chess Club
= 6 u - 3 u
= 3 u

3 u = 21

1 u = 21 ÷ 3 = 7

Number of members in Chess Club
= 8 u
= 8 x 7
= 56

Answer(s): 56