The ratio of the boys to the girls in a kindergarten was 7 : 3. After 20 boys went home and 29 new girls came, there were 7 more boys than girls in the end. Find the number of pupils in the kindergarten at first.
| |
Boys
(1) |
Girls
(2) |
(3) |
| Before |
7 u |
3 u |
3 u |
| Change |
- 20 |
+ 29 |
+ 29 + 7 = + 36 |
| After |
7 u |
3 u + 29 |
3 u + 36 |
Comparing boys and
girls in the end |
7 more |
|
|
Since the number of boys is 7 more than the number of girls in the end, when we
add 7 to (2) to form (3), the number of boys and girls in the end will be the same.
(1) = (3)
7 u - 20 = 3 u + 36
7 u - 3 u = 36 + 20
4 u = 56
1 u = 56 ÷ 4 = 14
Number of pupils at first
= 7 u + 3 u
= 10 u
= 10 x 14
= 140
Answer(s): 140
