Concert took in $162000. Tickets were $8.50 per student and $12.50 per adult. Total if 15000 people attended. How many adults came to the concert?
adults --- a
students ---s
a+s = 15000 or s = 15000-a
12.5a + 8.5s = 162000
times 2
25a + 17s = 324000
sub s = ...
25a + 17(15000-a) = 324000
25a - 17a =324000 - 255000
8a = 69000
a = 8625
s = 15000 - 8625 = 6375
so 8625 adults and 6375 students
check:
8625(12.50) + 6375(8.50) = 162000, check!