PSLE
The contestants at a contest are divided in Group A and Group B. The ratio of the number of boys to girls in Group A is 5 : 4. The ratio of the number of boys to girls in Group B is 5 : 1. There are 2 times as many contestants in Group B as in Group A. There are 150 less boys in Group A than Group B. What is the total number of contestants in Group A?

Group A		Group B
9 u		6x3 = 18 u
Boys	Girls	Boys	Girls
5 u	4 u	5x3 = 15 u	1x3 = 3 u

Total number of contestants in Group A
= 5 u + 4 u
= 9 u

Total number of contestants in Group B
= 2 x 9 u
= 18 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 18 and 6 is 18.

Number of less boys in Group A than Group B
= 15 u - 5 u
= 10 u

10 u = 150

1 u = 150 ÷ 10 = 15

Total number of contestants in Group A
= 5 u + 4 u
= 9 u
= 9 x 15
= 135

Answer(s): 135