PSLE
In a school, 30% of the members in Literary Club and 70% of the members in Chess Club are boys. Both clubs have the same number of girls. The Chess Club has 120 more boys than the Literary Club. How many boys are there altogether?

	Literary Club		Chess Club
Types	Boys	Girls	Boys	Girls
Comparing the boys and the girls in each club	3x3	7x3	7x7	3x7
Comparing the girls in 2 clubs		1		1
	9 u	21 u	49 u	21 u

30% = ³⁰₁₀₀ = ³₁₀

Fraction of the members in Literary Club that are girls
= 1 - ³₁₀
= ⁷₁₀

70% = ⁷⁰₁₀₀ = ⁷₁₀

Fraction of the members in Chess club that are girls
= 1 - ⁷₁₀
= ³₁₀

The number of girls in both clubs is the same. Make the numerators the same. LCM of 7 and 3 is 21. 

7x310x3 of the members in Literary Club = 3x710x7 of the members in Chess Club
2130of the members in Literary Club = 2170 of the members in Chess Club

Number of more boys in Chess Club than Literary Club
= 49 u - 9 u
= 40 u

40 u = 120

1 u = 120 ÷ 40 = 3

Total number of boys
= 9 u + 49 u
= 58 u
= 58 x 3
= 174

Answer(s): 174