The number of boys to the number of girls in Primary 1 Love was 1 : 4. The number of boys to the number of girls in Primary 1 Joy was 5 : 6. Both classes had the same number of boys. When 40 girls from Primary 1 Love joined Primary 1 Joy, the ratio of the number of boys to the number of girls in Primary 1 Love became 1 : 2. Find the total enrolment of both classes.

Primary 1 Love		Primary 1 Joy
Boys	Girls	Boys	Girls
1x5	4x5	5x1	6x1
1x5		1x5
5 u	20 u	5 u	6 u

The number of boys in both classes is the same.  Make the number of boys the same.  LCM of 1 and 5 is 5.

	Primary 1 Love		Primary 1 Joy
	Boys	Girls	Boys	Girls
Before	5 u	20 u	5 u	6 u
Change		- 40		+ 40
After	1x5 = 5 u	2x5 = 10 u	5 u	6 u + 40

The number of boys in Primary 1 Love remains unchanged.  Make the number of boys in Primary 1 the same.  LCM of 5 and 1 is 5.

Number of girls from Primary 1 Love that joined Primary 1 Joy
= 20 u - 10 u
= 10 u

10 u = 40

1 u = 40 ÷ 10 = 4

Total enrolment of both classes
= 5 u + 20 u + 5 u + 6 u
= 36 u
= 36 x 4
= 144

Answer(s): 144