The number of boys to the number of girls in Primary 5 Gentleness was 2 : 5. The number of boys to the number of girls in Primary 5 Kindness was 3 : 4. Both classes had the same number of boys. When 28 girls from Primary 5 Gentleness joined Primary 5 Kindness, the ratio of the number of boys to the number of girls in Primary 5 Gentleness became 3 : 4. Find the total enrolment of both classes.
Primary 5 Gentleness |
Primary 5 Kindness |
Boys |
Girls |
Boys |
Girls |
2x3 |
5x3 |
3x2 |
4x2 |
1x6 |
|
1x6 |
|
6 u |
15 u |
6 u |
8 u |
The number of boys in both classes is the same. Make the number of boys the same. LCM of 2 and 3 is 6.
|
Primary 5 Gentleness |
Primary 5 Kindness |
|
Boys |
Girls |
Boys |
Girls |
Before |
6 u |
15 u |
6 u |
8 u |
Change |
|
- 28 |
|
+ 28 |
After |
3x2 = 6 u |
4x2 = 8 u |
6 u |
8 u + 28 |
The number of boys in Primary 5 Gentleness remains unchanged. Make the number of boys in Primary 5 the same. LCM of 6 and 3 is 6.
Number of girls from Primary 5 Gentleness that joined Primary 5 Kindness
= 15 u - 8 u
= 7 u
7 u = 28
1 u = 28 ÷ 7 = 4
Total enrolment of both classes
= 6 u + 15 u + 6 u + 8 u
= 35 u
= 35 x 4
= 140
Answer(s): 140