19 of the visitors at a bird park were girls. 70% of the remaining visitors were boys and the rest were adults. The number of boys was 187 more than the total number of girls and adults. After some boys left the bird park, 50% of the visitors that remained were boys. How many boys left the bird park?
Girls |
Adults |
Boys |
Total |
1x5 |
8x5 |
9x5 |
|
3x4 |
7x4 |
|
5 |
12 |
28 |
45 |
|
Girls and adults |
Boys |
Before |
17x1 = 17 u |
28x1 = 28 u |
Change |
|
- 11 u |
After
|
1x17 = 17 u |
1x17 = 17 u |
70% =
70100 =
710 Adults : Boys = 3 : 7
The total number of adults and boys at first is repeated. Make the total number of adults at first the same. LCM of 8 and 10 is 40.
50% =
50100 =
12 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 17 and 1 is 17.
The number of boys was 187 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
= 28 u - 17 u
= 11 u
11 u = 187
1 u = 187 ÷ 11 = 17
Number of boys who left the bird park
= 28 u - 17 u
= 11 u
= 11 x 17
= 187
Answer(s): 187