PSLE
In a school, 30% of the members in Reading Club and 80% of the members in Computer Club are girls. Both clubs have the same number of boys. The Computer Club has 100 more girls than the Reading Club. How many girls are there altogether?

	Reading Club		Computer Club
Types	Girls	Boys	Girls	Boys
Comparing the girls and the boys in each club	3x1	7x1	4x7	1x7
Comparing the boys in 2 clubs		1		1
	3 u	7 u	28 u	7 u

30% = ³⁰₁₀₀ = ³₁₀

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

80% = ⁸⁰₁₀₀ = ⁴₅

Fraction of the members in Computer club that are boys
= 1 - ⁴₅
= ¹₅

The number of boys in both clubs is the same. Make the numerators the same. LCM of 7 and 1 is 7. 

7x110x1 of the members in Reading Club = 1x75x7 of the members in Computer Club
710of the members in Reading Club = 735 of the members in Computer Club

Number of more girls in Computer Club than Reading Club
= 28 u - 3 u
= 25 u

25 u = 100

1 u = 100 ÷ 25 = 4

Total number of girls
= 3 u + 28 u
= 31 u
= 31 x 4
= 124

Answer(s): 124