The number of girls to the number of boys in Primary 1 Patience was 1 : 4. The number of girls to the number of boys in Primary 1 Love was 5 : 6. Both classes had the same number of girls. When 20 boys from Primary 1 Patience joined Primary 1 Love, the ratio of the number of girls to the number of boys in Primary 1 Patience became 1 : 3. Find the total enrolment of both classes.

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

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

	Primary 1 Patience		Primary 1 Love
	Girls	Boys	Girls	Boys
Before	5 u	20 u	5 u	6 u
Change		- 20		+ 20
After	1x5 = 5 u	3x5 = 15 u	5 u	6 u + 20

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

Number of boys from Primary 1 Patience that joined Primary 1 Love
= 20 u - 15 u
= 5 u

5 u = 20

1 u = 20 ÷ 5 = 4

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

Answer(s): 144