The number of boys to the number of girls in Primary 1 Peace was 1 : 4. The number of boys to the number of girls in Primary 1 Kindness was 3 : 5. Both classes had the same number of boys. When 42 girls from Primary 1 Peace joined Primary 1 Kindness, the ratio of the number of boys to the number of girls in Primary 1 Peace became 1 : 2. Find the total enrolment of both classes.
Primary 1 Peace |
Primary 1 Kindness |
Boys |
Girls |
Boys |
Girls |
1x3 |
4x3 |
3x1 |
5x1 |
1x3 |
|
1x3 |
|
3 u |
12 u |
3 u |
5 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 1 Peace |
Primary 1 Kindness |
|
Boys |
Girls |
Boys |
Girls |
Before |
3 u |
12 u |
3 u |
5 u |
Change |
|
- 42 |
|
+ 42 |
After |
1x3 = 3 u |
2x3 = 6 u |
3 u |
5 u + 42 |
The number of boys in Primary 1 Peace remains unchanged. Make the number of boys in Primary 1 the same. LCM of 3 and 1 is 3.
Number of girls from Primary 1 Peace that joined Primary 1 Kindness
= 12 u - 6 u
= 6 u
6 u = 42
1 u = 42 ÷ 6 = 7
Total enrolment of both classes
= 3 u + 12 u + 3 u + 5 u
= 23 u
= 23 x 7
= 161
Answer(s): 161