At first, the ratio of the number of girls to the number of boys at a stadium was 3 : 7. When 42 boys and some girls entered the stadium, the number of boys increased by 10% and the total number of children at the stadium increased by 20%.
- How many girls were there at first?
- What percentage of the children at the stadium were girls in the end? Express your answer as a mixed number.
(a)
Girls |
Boys |
Total |
3 u |
7 u |
10 u |
(+ 78) |
+ 0.7 u (+ 42) |
+ 2 u (+ 120) |
3 u + 78 |
7.7 u |
12 u |
Number of boys that entered the stadium
= 10% x 7 u
=
10100 x 7 u
= 0.7 u
0.7 u = 42
1 u = 42 ÷ 0.7 = 60
Number of girls at first
= 3 u
= 3 x 60
= 180
(b)
Increase in the number of children
= 20% x 10 u
=
20100 x 10 u
= 2 u
Total number of children at the stadium in the end
= 10 u + 2 u
= 12 u
= 12 x 60
= 720
Increase in the number of girls
= 120 - 42
= 78
Total number of girls in the end
= 3 u + 78
= 3 x 60 + 78
= 258
Percentage of children who were girls
=
258720 x 100
= 35
56%
Answer(s): (a) 180; (b) 35
56%