PSLE
The contestants at a contest are divided in Group A and Group B. The ratio of the number of girls to boys in Group A is 7 : 1. The ratio of the number of girls to boys in Group B is 5 : 1. There are 3 times as many contestants in Group B as in Group A. There are 143 more girls in Group B than Group A. What is the total number of boys?

Group A		Group B
8 u		6x4 = 24 u
Girls	Boys	Girls	Boys
7 u	1 u	5x4 = 20 u	1x4 = 4 u

Total number of contestants in Group A
= 7 u + 1 u
= 8 u

Total number of contestants in Group B
= 3 x 8 u
= 24 u

The total number of contestants in Group B is repeated.
Use LCM to make the total number of contestants in Group B the same.
LCM of 24 and 6 is 24.

Number of more girls in Group B than Group A
= 20 u - 7 u
= 13 u

13 u = 143

1 u = 143 ÷ 13 = 11

Total number of boys
= 1 u + 4 u
= 5 u
= 5 x 11
= 55

Answer(s): 55