The number of girls to the number of boys in Primary 1 Love was 2 : 5. The number of girls to the number of boys in Primary 1 Faithfulness was 3 : 5. Both classes had the same number of girls. When 15 boys from Primary 1 Love joined Primary 1 Faithfulness, the ratio of the number of girls to the number of boys in Primary 1 Love became 3 : 5. Find the total enrolment of both classes.

Primary 1 Love		Primary 1 Faithfulness
Girls	Boys	Girls	Boys
2x3	5x3	3x2	5x2
1x6		1x6
6 u	15 u	6 u	10 u

The number of girls in both classes is the same.  Make the number of girls the same.  LCM of 2 and 3 is 6.

	Primary 1 Love		Primary 1 Faithfulness
	Girls	Boys	Girls	Boys
Before	6 u	15 u	6 u	10 u
Change		- 15		+ 15
After	3x2 = 6 u	5x2 = 10 u	6 u	10 u + 15

The number of girls in Primary 1 Love remains unchanged.  Make the number of girls in Primary 1 the same.  LCM of 6 and 3 is 6.

Number of boys from Primary 1 Love that joined Primary 1 Faithfulness
= 15 u - 10 u
= 5 u

5 u = 15

1 u = 15 ÷ 5 = 3

Total enrolment of both classes
= 6 u + 15 u + 6 u + 10 u
= 37 u
= 37 x 3
= 111

Answer(s): 111