PSLE
The number of boys and girls taking part in a test are in the ratio 1 : 8. These students are put into two groups. 80% of the boys and 20% of the girls are in Group N. The rest of the students are in Group P.

1. What is the ratio of the number of students in Group P to Group N? Give your answer in the simplest form.
2. The number of girls in Group N is more than 60. What is the smallest possible total number of students taking part in the test?

Boys		Girls
10 u		80 u
Group N	Group P	Group N	Group P
8 u	2 u	16 u	64 u

(a)
Boys : Girls
1 : 8
10 : 80

Number of boys in Group N
= 80% x 10 u
= ⁸⁰₁₀₀ x 10 u
= 8 u

Number of boys in Group P
= 10 u - 8 u
= 2 u

Number of girls in Group N
= 20% x 80 u
= ²⁰₁₀₀ x 80 u
= 16 u

Number of girls in Group P
= 80 u - 16 u
= 64 u

Group N : Group P
2 + 64 : 8 + 16 
66 : 24 _(÷6)
11 : 4

(b)
Number of girls in Group N = 16 u

Since the number of girls in Group N is 16 u, it must be multiple of 16.

Number of sets of 16
= 60 ÷ 16
= 3 r 12

Since the number of girls in Group N is more than 60, the number of sets must be 1 more than 3.

1 u = 3 + 1 = 4

Smallest possible number of students
= 10 u + 80 u
= 90 u
= 90 x 4
= 360

Answer(s): (a) 11 : 4; (b) 360