PSLE
The number of girls and boys taking part in a test are in the ratio 3 : 4. These students are put into two teams. 30% of the girls and 40% of the boys are in Team R. The rest of the students are in Team S.

1. What is the ratio of the number of students in Team S to Team R? Give your answer in the simplest form.
2. The number of girls in Team S is fewer than 70. What is the largest possible total number of students taking part in the test?

Girls		Boys
30 u		40 u
Team R	Team S	Team R	Team S
9 u	21 u	16 u	24 u

(a)
Girls : Boys
3 : 4
30 : 40

Number of girls in Team R
= 30% x 30 u
= ³⁰₁₀₀ x 30 u
= 9 u

Number of girls in Team S
= 30 u - 9 u
= 21 u

Number of boys in Team R
= 40% x 40 u
= ⁴⁰₁₀₀ x 40 u
= 16 u

Number of boys in Team S
= 40 u - 16 u
= 24 u

Team S : Team R
21 + 24 : 9 + 16
45 : 25 _(÷5)
9 : 5

(b)
Number of girls in Team S = 21 u

Since the number of girls in Team S is 21 u, it must be multiple of 21.

Number of sets of 21
= 70 ÷ 21
= 3 r 7

Since the number of girls in Team S is less than 70, the number of sets must be 3.

1 u = 3

Largest possible number of students
= 30 u + 40 u
= 70 u
= 70 x 3
= 210

Answer(s): (a) 9 : 5; (b) 210