PSLE
The number of girls and boys taking part in a test are in the ratio 7 : 5. These pupils are put into two teams. 10% of the girls and 40% of the boys are in Team A. The rest of the pupils are in Team B.

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

Girls		Boys
70 u		50 u
Team A	Team B	Team A	Team B
7 u	63 u	20 u	30 u

(a)
Girls : Boys
7 : 5
70 : 50

Number of girls in Team A
= 10% x 70 u
= ¹⁰₁₀₀ x 70 u
= 7 u

Number of girls in Team B
= 70 u - 7 u
= 63 u

Number of boys in Team A
= 40% x 50 u
= ⁴⁰₁₀₀ x 50 u
= 20 u

Number of boys in Team B
= 50 u - 20 u
= 30 u

Team A : Team B
63 + 30 : 7 + 20 
93 : 27 _(÷3)
31 : 9

(b)
Number of boys in Team A = 20 u

Since the number of boys in Team A is 20 u, it must be multiple of 20.

Number of sets of 20
= 90 ÷ 20
= 4 r 10

Since the number of boys in Team A is more than 90, the number of sets must be 1 more than 4.

1 u = 4 + 1 = 5

Smallest possible number of pupils
= 70 u + 50 u
= 120 u
= 120 x 5
= 600

Answer(s): (a) 31 : 9; (b) 600