The number of boys to the number of girls in Primary 3 Peace was 1 : 4. The number of boys to the number of girls in Primary 3 Gentleness was 2 : 5. Both classes had the same number of boys. When 20 girls from Primary 3 Peace joined Primary 3 Gentleness, the ratio of the number of boys to the number of girls in Primary 3 Peace became 1 : 2. Find the total enrolment of both classes.
Primary 3 Peace |
Primary 3 Gentleness |
Boys |
Girls |
Boys |
Girls |
1x2 |
4x2 |
2x1 |
5x1 |
1x2 |
|
1x2 |
|
2 u |
8 u |
2 u |
5 u |
The number of boys in both classes is the same. Make the number of boys the same. LCM of 1 and 2 is 2.
|
Primary 3 Peace |
Primary 3 Gentleness |
|
Boys |
Girls |
Boys |
Girls |
Before |
2 u |
8 u |
2 u |
5 u |
Change |
|
- 20 |
|
+ 20 |
After |
1x2 = 2 u |
2x2 = 4 u |
2 u |
5 u + 20 |
The number of boys in Primary 3 Peace remains unchanged. Make the number of boys in Primary 3 the same. LCM of 2 and 1 is 2.
Number of girls from Primary 3 Peace that joined Primary 3 Gentleness
= 8 u - 4 u
= 4 u
4 u = 20
1 u = 20 ÷ 4 = 5
Total enrolment of both classes
= 2 u + 8 u + 2 u + 5 u
= 17 u
= 17 x 5
= 85
Answer(s): 85