The number of boys to the number of girls in Primary 3 Goodness was 2 : 5. The number of boys to the number of girls in Primary 3 Patience was 5 : 6. Both classes had the same number of boys. When 27 girls from Primary 3 Goodness joined Primary 3 Patience, the ratio of the number of boys to the number of girls in Primary 3 Goodness became 5 : 8. Find the total enrolment of both classes.

Primary 3 Goodness		Primary 3 Patience
Boys	Girls	Boys	Girls
2x5	5x5	5x2	6x2
1x10		1x10
10 u	25 u	10 u	12 u

The number of boys in both classes is the same.  Make the number of boys the same.  LCM of 2 and 5 is 10.

	Primary 3 Goodness		Primary 3 Patience
	Boys	Girls	Boys	Girls
Before	10 u	25 u	10 u	12 u
Change		- 27		+ 27
After	5x2 = 10 u	8x2 = 16 u	10 u	12 u + 27

The number of boys in Primary 3 Goodness remains unchanged.  Make the number of boys in Primary 3 the same.  LCM of 10 and 5 is 10.

Number of girls from Primary 3 Goodness that joined Primary 3 Patience
= 25 u - 16 u
= 9 u

9 u = 27

1 u = 27 ÷ 9 = 3

Total enrolment of both classes
= 10 u + 25 u + 10 u + 12 u
= 57 u
= 57 x 3
= 171

Answer(s): 171