PSLE
The pupils at a camp are divided in Group A and Group B. The ratio of the number of boys to girls in Group A is 3 : 1. The ratio of the number of boys to girls in Group B is 9 : 1. There are 5 times as many pupils in Group B as in Group A. There are 30 more boys in Group B than Group A. What is the total number of pupils?

Group A		Group B
4 u		10x2 = 20 u
Boys	Girls	Boys	Girls
3 u	1 u	9x2 = 18 u	1x2 = 2 u

Total number of pupils in Group A
= 3 u + 1 u
= 4 u

Total number of pupils in Group B
= 5 x 4 u
= 20 u

The total number of pupils in Group B is repeated.
Use LCM to make the total number of pupils in Group B the same.
LCM of 20 and 10 is 20.

Number of more boys in Group B than Group A
= 18 u - 3 u
= 15 u

15 u = 30

1 u = 30 ÷ 15 = 2

Total number of pupils
= 3 u + 1 u + 18 u + 2 u
= 24 u
= 24 x 2
= 48

Answer(s): 48