The number of boys to the number of girls in Primary 3 Kindness was 1 : 4. The number of boys to the number of girls in Primary 3 Joy was 2 : 5. Both classes had the same number of boys. When 28 girls from Primary 3 Kindness joined Primary 3 Joy, the ratio of the number of boys to the number of girls in Primary 3 Kindness became 1 : 2. Find the total enrolment of both classes.
Primary 3 Kindness |
Primary 3 Joy |
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 Kindness |
Primary 3 Joy |
|
Boys |
Girls |
Boys |
Girls |
Before |
2 u |
8 u |
2 u |
5 u |
Change |
|
- 28 |
|
+ 28 |
After |
1x2 = 2 u |
2x2 = 4 u |
2 u |
5 u + 28 |
The number of boys in Primary 3 Kindness 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 Kindness that joined Primary 3 Joy
= 8 u - 4 u
= 4 u
4 u = 28
1 u = 28 ÷ 4 = 7
Total enrolment of both classes
= 2 u + 8 u + 2 u + 5 u
= 17 u
= 17 x 7
= 119
Answer(s): 119