PSLE
The number of girls and boys taking part in a contest are in the ratio 2 : 7. These pupils are put into two teams. 50% of the girls and 40% of the boys are in Team B. The rest of the pupils are in Team C.

1. What is the ratio of the number of pupils in Team C to Team B? Give your answer in the simplest form.
2. The number of boys in Team B is more than 90. What is the smallest possible total number of pupils taking part in the contest?

Girls		Boys
20 u		70 u
Team B	Team C	Team B	Team C
10 u	10 u	28 u	42 u

(a)
Girls : Boys
2 : 7
20 : 70

Number of girls in Team B
= 50% x 20 u
= ⁵⁰₁₀₀ x 20 u
= 10 u

Number of girls in Team C
= 20 u - 10 u
= 10 u

Number of boys in Team B
= 40% x 70 u
= ⁴⁰₁₀₀ x 70 u
= 28 u

Number of boys in Team C
= 70 u - 28 u
= 42 u

Team B : Team C
10 + 42 : 10 + 28 
52 : 38 _(÷2)
26 : 19

(b)
Number of boys in Team B = 28 u

Since the number of boys in Team B is 28 u, it must be multiple of 28.

Number of sets of 28
= 90 ÷ 28
= 3 r 6

Since the number of boys in Team B is more than 90, the number of sets must be 1 more than 3.

1 u = 3 + 1 = 4

Smallest possible number of pupils
= 20 u + 70 u
= 90 u
= 90 x 4
= 360

Answer(s): (a) 26 : 19; (b) 360