25% of the people are performers for a concert and the rest are spectators. 70% of the spectators are parents and there are 1920 less child spectators than parent spectators. How many parent spectators must join so that 81% of the people are parent spectators?
|
Performers |
Spectators |
|
1x10 |
3x10 |
|
|
Children |
Parents |
|
|
3x3 |
7x3 |
Before |
10 u |
9 u |
21 u |
Change |
|
|
+ ? |
After |
19x1 = 19 u |
81x1 = 81 u |
25% =
25100 =
14 70% =
70100 =
710 81% =
81100 =
81100The total number of spectators at first is repeated. Make the total number of spectators the same. LCM of 3 and 10 is 30.
Number of less child spectators than parent spectators at first
= 21 u - 9 u
= 12 u
12 u = 1920
1 u = 1920 ÷ 12 = 160
If some parent spectators join, the total number of child spectators and performers remains unchanged.
Number of parent spectators who must join so that 81% of the people are parent spectators
= 81 u - 21 u
= 60 u
= 60 x 160
= 9600
Answer(s): 9600