PSLE
In a school, 50% of the members in Chess Club and 70% of the members in Literary Club are girls. Both clubs have the same number of boys. The Literary Club has 40 more girls than the Chess Club. How many girls are there altogether?

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

50% = ⁵⁰₁₀₀ = ¹₂

Fraction of the members in Chess Club that are boys
= 1 - ¹₂
= ¹₂

70% = ⁷⁰₁₀₀ = ⁷₁₀

Fraction of the members in Literary club that are boys
= 1 - ⁷₁₀
= ³₁₀

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

1x32x3 of the members in Chess Club = 3x110x1 of the members in Literary Club
36of the members in Chess Club = 310 of the members in Literary Club

Number of more girls in Literary Club than Chess Club
= 7 u - 3 u
= 4 u

4 u = 40

1 u = 40 ÷ 4 = 10

Total number of girls
= 3 u + 7 u
= 10 u
= 10 x 10
= 100

Answer(s): 100