PSLE The number of boys and girls in a music room were in the ratio 2 : 5. After 4.5 boys entered the music room and half the number of girls left the music room, the ratio of the number of boys to girls became 1 : 1. How many children were there in the music room at first?
|
boys |
girls |
Total |
Before |
2 u |
5 u |
7 u |
Change |
+ 4.5 |
- 2.5 u |
|
After |
2 u + 4.5 |
2.5 u |
|
Number of girls who left the music room
= 5 u ÷ 2
= 2.5 u
Number of boys in the end = 2 u + 4.5
Number of girls in the end = 2.5 u
Since the ratio of the number of boys to girls in the end is 1 : 1, the number of boys and girls in the end is equal.
2.5 u = 2 u + 4.5
2.5 u - 2 u = 4.5
0.5 u = 4.5
1 u = 4.5 ÷ 0.5 = 9
Total number of children in the music room at first
= 2 u + 5 u
= 7 u
= 7 x 9
= 63
Answer(s): 63