PSLE
The number of girls and boys taking part in a contest are in the ratio 4 : 7. These pupils are put into two teams. 10% of the girls and 30% of the boys are in Team C. The rest of the pupils are in Team D.

1. What is the ratio of the number of pupils in Team D to Team C? Give your answer in the simplest form.
2. The number of girls in Team D is fewer than 80. What is the largest possible total number of pupils taking part in the contest?

Girls		Boys
40 u		70 u
Team C	Team D	Team C	Team D
4 u	36 u	21 u	49 u

(a)
Girls : Boys
4 : 7
40 : 70

Number of girls in Team C
= 10% x 40 u
= ¹⁰₁₀₀ x 40 u
= 4 u

Number of girls in Team D
= 40 u - 4 u
= 36 u

Number of boys in Team C
= 30% x 70 u
= ³⁰₁₀₀ x 70 u
= 21 u

Number of boys in Team D
= 70 u - 21 u
= 49 u

Team D : Team C
36 + 49 : 4 + 21
85 : 25 _(÷5)
17 : 5

(b)
Number of girls in Team D = 36 u

Since the number of girls in Team D is 36 u, it must be multiple of 36.

Number of sets of 36
= 80 ÷ 36
= 2 r 8

Since the number of girls in Team D is less than 80, the number of sets must be 2.

1 u = 2

Largest possible number of pupils
= 40 u + 70 u
= 110 u
= 110 x 2
= 220

Answer(s): (a) 17 : 5; (b) 220