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

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

30% = ³⁰₁₀₀ = ³₁₀

Fraction of the members in Computer Club that are boys
= 1 - ³₁₀
= ⁷₁₀

70% = ⁷⁰₁₀₀ = ⁷₁₀

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

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

7x310x3 of the members in Computer Club = 3x710x7 of the members in Art Club
2130of the members in Computer Club = 2170 of the members in Art Club

Number of more girls in Art Club than Computer Club
= 49 u - 9 u
= 40 u

40 u = 120

1 u = 120 ÷ 40 = 3

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

Answer(s): 174