At first, the ratio of the number of boys to the number of girls at a bird park was 2 : 5. When 54 girls and some boys entered the bird park, the number of girls increased by 10% and the total number of children at the bird park increased by 25%.
- How many boys were there at first?
- What percentage of the children at the bird park were boys in the end? Express your answer as a mixed number.
(a)
Boys |
Girls |
Total |
2 u |
5 u |
7 u |
(+ 135) |
+ 0.5 u (+ 54) |
+ 1.75 u (+ 189) |
2 u + 135 |
5.5 u |
8.75 u |
Number of girls that entered the bird park
= 10% x 5 u
=
10100 x 5 u
= 0.5 u
0.5 u = 54
1 u = 54 ÷ 0.5 = 108
Number of boys at first
= 2 u
= 2 x 108
= 216
(b)
Increase in the number of children
= 25% x 7 u
=
25100 x 7 u
= 1.75 u
Total number of children at the bird park in the end
= 7 u + 1.75 u
= 8.75 u
= 8.75 x 108
= 945
Increase in the number of boys
= 189 - 54
= 135
Total number of boys in the end
= 2 u + 135
= 2 x 108 + 135
= 351
Percentage of children who were boys
=
351945 x 100
= 37
17%
Answer(s): (a) 216; (b) 37
17%