The ratio of the boys to the girls in a kindergarten was 7 : 2. After 13 boys went home and 19 new girls came, there were 18 more boys than girls in the end. Find the number of students in the kindergarten at first.
| |
Boys
(1) |
Girls
(2) |
(3) |
| Before |
7 u |
2 u |
2 u |
| Change |
- 13 |
+ 19 |
+ 19 + 18 = + 37 |
| After |
7 u |
2 u + 19 |
2 u + 37 |
Comparing boys and
girls in the end |
18 more |
|
|
Since the number of boys is 18 more than the number of girls in the end, when we
add 18 to (2) to form (3), the number of boys and girls in the end will be the same.
(1) = (3)
7 u - 13 = 2 u + 37
7 u - 2 u = 37 + 13
5 u = 50
1 u = 50 ÷ 5 = 10
Number of students at first
= 7 u + 2 u
= 9 u
= 9 x 10
= 90
Answer(s): 90
