The number of girls to the number of boys in Primary 3 Goodness was 3 : 5. The number of girls to the number of boys in Primary 3 Kindness was 4 : 5. Both classes had the same number of girls. When 12 boys from Primary 3 Goodness joined Primary 3 Kindness, the ratio of the number of girls to the number of boys in Primary 3 Goodness became 6 : 7. Find the total enrolment of both classes.
Primary 3 Goodness |
Primary 3 Kindness |
Girls |
Boys |
Girls |
Boys |
3x4 |
5x4 |
4x3 |
5x3 |
1x12 |
|
1x12 |
|
12 u |
20 u |
12 u |
15 u |
The number of girls in both classes is the same. Make the number of girls the same. LCM of 3 and 4 is 12.
|
Primary 3 Goodness |
Primary 3 Kindness |
|
Girls |
Boys |
Girls |
Boys |
Before |
12 u |
20 u |
12 u |
15 u |
Change |
|
- 12 |
|
+ 12 |
After |
6x2 = 12 u |
7x2 = 14 u |
12 u |
15 u + 12 |
The number of girls in Primary 3 Goodness remains unchanged. Make the number of girls in Primary 3 the same. LCM of 12 and 6 is 12.
Number of boys from Primary 3 Goodness that joined Primary 3 Kindness
= 20 u - 14 u
= 6 u
6 u = 12
1 u = 12 ÷ 6 = 2
Total enrolment of both classes
= 12 u + 20 u + 12 u + 15 u
= 59 u
= 59 x 2
= 118
Answer(s): 118