PSLE
In a school, 70% of the members in Drama Club and 90% of the members in Reading Club are girls. Both clubs have the same number of boys. The Reading Club has 80 more girls than the Drama Club. How many girls are there altogether?

	Drama Club		Reading Club
Types	Girls	Boys	Girls	Boys
Comparing the girls and the boys in each club	7x1	3x1	9x3	1x3
Comparing the boys in 2 clubs		1		1
	7 u	3 u	27 u	3 u

70% = ⁷⁰₁₀₀ = ⁷₁₀

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

90% = ⁹⁰₁₀₀ = ⁹₁₀

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

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

3x110x1 of the members in Drama Club = 1x310x3 of the members in Reading Club
310of the members in Drama Club = 330 of the members in Reading Club

Number of more girls in Reading Club than Drama Club
= 27 u - 7 u
= 20 u

20 u = 80

1 u = 80 ÷ 20 = 4

Total number of girls
= 7 u + 27 u
= 34 u
= 34 x 4
= 136

Answer(s): 136