29 of the people at a bird park were boys. 90% of the remaining people were girls and the rest were adults. The number of girls was 648 more than the total number of boys and adults. After some girls left the bird park, 50% of the people that remained were girls. How many girls left the bird park?
Boys |
Adults |
Girls |
Total |
2x10 |
7x10 |
9x10 |
|
1x7 |
9x7 |
|
20 |
7 |
63 |
90 |
|
Boys and adults |
Girls |
Before |
27x1 = 27 u |
63x1 = 63 u |
Change |
|
- 36 u |
After
|
1x27 = 27 u |
1x27 = 27 u |
90% =
90100 =
910 Adults : Girls = 1 : 9
The total number of adults and girls at first is repeated. Make the total number of adults at first the same. LCM of 7 and 10 is 70.
50% =
50100 =
12 When some girls left, the total number of boys and adults remains unchanged. Make the total number of boys and adults the same. LCM of 27 and 1 is 27.
The number of girls was 648 more than the total number of boys and adults at first.
Number of more girls than the total number of boys and adults at first
= 63 u - 27 u
= 36 u
36 u = 648
1 u = 648 ÷ 36 = 18
Number of girls who left the bird park
= 63 u - 27 u
= 36 u
= 36 x 18
= 648
Answer(s): 648