PSLE
In a school, 60% of the members in Literary Club and 90% of the members in Chess Club are girls. Both clubs have the same number of boys. The Chess Club has 75 more girls than the Literary Club. How many girls are there altogether?

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

60% = ⁶⁰₁₀₀ = ³₅

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

90% = ⁹⁰₁₀₀ = ⁹₁₀

Fraction of the members in Chess club that are boys
= 1 - ⁹₁₀
= ¹₁₀

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 = 1x210x2 of the members in Chess Club
25of the members in Literary Club = 220 of the members in Chess Club

Number of more girls in Chess Club than Literary Club
= 18 u - 3 u
= 15 u

15 u = 75

1 u = 75 ÷ 15 = 5

Total number of girls
= 3 u + 18 u
= 21 u
= 21 x 5
= 105

Answer(s): 105