Tom K. answered 01/14/19
Knowledgeable and Friendly Math and Statistics Tutor
O = orchestra seats at $50
M = main seats at $30
B = balcony seats at $25
400 seats, so (1) O + M + B = 400
(2) 50 O + 30 M + 25 B = 13000
(3) 1/2 (50 O) + 30 M + 25 B = 11000
Subtract equation 3 from equation 2
1/2(50 O) = 13000 - 11000
25O = 2000
O = 80
Subtract from (1)
M + B = 320
Subtract 25O = 2000 from (3)
30M + 25 B = 9000
25M + 25B = (320)(25) = 8000
Subtracting, 5M = 1000
M = 200
B = 320 - M
B = 120