All 500 seats to the Friday Night Seniors' Play were sold, and a total of $3312.50 was collected. If adult ticket cost 7.50 each and Senior tickets cost $4 each, how many bills of each type were sold?

Respuesta :

a + s = 500.....a = 500 - s
7.5a + 4s = 3312.50

7.5(500 - s) + 4s = 3312.50
3750 - 7.5s + 4s = 3312.50
-7.5s + 4s = 3312.50 - 3750
-3.5s = - 437.50
s = -437.50/-3.5
s = 125 <=== 125 senior tickets

a = 500 - s
a = 500 - 125
a = 375 <=== 375 adult tickets
yes that's right but how do we know it's not s=375 and a=124