For this case we propose a system of equations:
x: Let the variable representing the number of children in the concert
y: Let the variable representing the number of adults at the concert
According to the assistance we have:
[tex]x = 3y[/tex]
According to the cost we have:
[tex]3x + 7y = 6000[/tex]
Substituting the first in the second equation we have:
[tex]3 (3y) + 7y = 6000\\9y + 7y = 6000\\16y = 6000\\y = \frac {6000} {16}\\y = 375[/tex]
Thus, the concert was 375 adults.
On the other hand we have:
[tex]x = 3 (375) = 1125[/tex]
Thus, the concert was 1125 children.
In total they were:
[tex]375 + 1125 = 1500[/tex] people
ANswer:
The concert was 1500 people
