The number of girls to the number of boys in Primary 5 Goodness was 2 : 5. The number of girls to the number of boys in Primary 5 Kindness was 3 : 4. Both classes had the same number of girls. When 30 boys from Primary 5 Goodness joined Primary 5 Kindness, the ratio of the number of girls to the number of boys in Primary 5 Goodness became 2 : 3. Find the total enrolment of both classes.
Primary 5 Goodness |
Primary 5 Kindness |
Girls |
Boys |
Girls |
Boys |
2x3 |
5x3 |
3x2 |
4x2 |
1x6 |
|
1x6 |
|
6 u |
15 u |
6 u |
8 u |
The number of girls in both classes is the same. Make the number of girls the same. LCM of 2 and 3 is 6.
|
Primary 5 Goodness |
Primary 5 Kindness |
|
Girls |
Boys |
Girls |
Boys |
Before |
6 u |
15 u |
6 u |
8 u |
Change |
|
- 30 |
|
+ 30 |
After |
2x3 = 6 u |
3x3 = 9 u |
6 u |
8 u + 30 |
The number of girls in Primary 5 Goodness remains unchanged. Make the number of girls in Primary 5 the same. LCM of 6 and 2 is 6.
Number of boys from Primary 5 Goodness that joined Primary 5 Kindness
= 15 u - 9 u
= 6 u
6 u = 30
1 u = 30 ÷ 6 = 5
Total enrolment of both classes
= 6 u + 15 u + 6 u + 8 u
= 35 u
= 35 x 5
= 175
Answer(s): 175