110 of the people at a zoo were girls. 80% of the remaining people were boys and the rest were adults. The number of boys was 990 more than the total number of girls and adults. After some boys left the zoo, 70% of the people that remained were boys. How many boys left the zoo?
Girls |
Adults |
Boys |
Total |
1x5 |
9x5 |
10x5 |
|
1x9 |
4x9 |
|
5 |
9 |
36 |
50 |
|
Girls and adults |
Boys |
Before |
14x3 = 42 u |
36x3 = 108 u |
Change |
|
- 10 u |
After
|
3x14 = 42 u |
7x14 = 98 u |
80% =
80100 =
45 Adults : Boys = 1 : 4
The total number of adults and boys at first is repeated. Make the total number of adults at first the same. LCM of 9 and 5 is 45.
70% =
70100 =
710 When some boys left, the total number of girls and adults remains unchanged. Make the total number of girls and adults the same. LCM of 14 and 3 is 42.
The number of boys was 990 more than the total number of girls and adults at first.
Number of more boys than the total number of girls and adults at first
= 108 u - 42 u
= 66 u
66 u = 990
1 u = 990 ÷ 66 = 15
Number of boys who left the zoo
= 108 u - 98 u
= 10 u
= 10 x 15
= 150
Answer(s): 150