The number of boys to the number of girls in Primary 1 Peace was 2 : 5. The number of boys to the number of girls in Primary 1 Patience was 3 : 5. Both classes had the same number of boys. When 12 girls from Primary 1 Peace joined Primary 1 Patience, the ratio of the number of boys to the number of girls in Primary 1 Peace became 2 : 3. Find the total enrolment of both classes.

Primary 1 Peace		Primary 1 Patience
Boys	Girls	Boys	Girls
2x3	5x3	3x2	5x2
1x6		1x6
6 u	15 u	6 u	10 u

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

	Primary 1 Peace		Primary 1 Patience
	Boys	Girls	Boys	Girls
Before	6 u	15 u	6 u	10 u
Change		- 12		+ 12
After	2x3 = 6 u	3x3 = 9 u	6 u	10 u + 12

The number of boys in Primary 1 Peace remains unchanged.  Make the number of boys in Primary 1 the same.  LCM of 6 and 2 is 6.

Number of girls from Primary 1 Peace that joined Primary 1 Patience
= 15 u - 9 u
= 6 u

6 u = 12

1 u = 12 ÷ 6 = 2

Total enrolment of both classes
= 6 u + 15 u + 6 u + 10 u
= 37 u
= 37 x 2
= 74

Answer(s): 74