The number of boys to the number of girls in Primary 2 Joy was 1 : 4. The number of boys to the number of girls in Primary 2 Gentleness was 3 : 4. Both classes had the same number of boys. When 30 girls from Primary 2 Joy joined Primary 2 Gentleness, the ratio of the number of boys to the number of girls in Primary 2 Joy became 1 : 2. Find the total enrolment of both classes.
Primary 2 Joy |
Primary 2 Gentleness |
Boys |
Girls |
Boys |
Girls |
1x3 |
4x3 |
3x1 |
4x1 |
1x3 |
|
1x3 |
|
3 u |
12 u |
3 u |
4 u |
The number of boys in both classes is the same. Make the number of boys the same. LCM of 1 and 3 is 3.
|
Primary 2 Joy |
Primary 2 Gentleness |
|
Boys |
Girls |
Boys |
Girls |
Before |
3 u |
12 u |
3 u |
4 u |
Change |
|
- 30 |
|
+ 30 |
After |
1x3 = 3 u |
2x3 = 6 u |
3 u |
4 u + 30 |
The number of boys in Primary 2 Joy remains unchanged. Make the number of boys in Primary 2 the same. LCM of 3 and 1 is 3.
Number of girls from Primary 2 Joy that joined Primary 2 Gentleness
= 12 u - 6 u
= 6 u
6 u = 30
1 u = 30 ÷ 6 = 5
Total enrolment of both classes
= 3 u + 12 u + 3 u + 4 u
= 22 u
= 22 x 5
= 110
Answer(s): 110