315 people went to a concert hall.
47 were children. Some adults joined halfway and the ratio of the number of children to the number of adults became 12 : 13. How many adults joined the concert hall halfway?
|
Children |
Adults |
Total |
Before |
4x3 = 12 u |
3x3 = 9 u |
7x3 = 21 u |
Change |
|
+ ? |
|
After |
12 u |
13 u |
|
Fraction of the people that were adults at first
= 1 -
47 =
37 Number of children remains unchanged. Make the number of children the same. LCM of 4 and 12 is 12.
Total number of people at first = 21 u
21 u = 315
1 u = 315 ÷ 21 = 15
Number of adults who joined halfway
= 13 u - 9 u
= 4 u
= 4 x 15
= 60
Answer(s): 60