Tickets to a certain concert sell for $20 each. The first 10 people to show up at the ticket booth received a 40% discount, and the next 20 received a 15% discount. If 50 people bought tickets to the concert, what was the total revenue from ticket sales? Choose the correct choice from the following options:  A) $ 600  B) $ 740  C) $ 860  D) $ 980  E) $ 1,140

Rationale: "price of 1 ticket = 20 $ revenue generated from sales of first 10 tickets = 10 * ( 60 / 100 * 20 ) = 10 * 12 = 120 revenue generated from sales of next 20 tickets = 20 * ( 85 / 100 * 20 ) = 20 * 17 = 340 revenue generated from sales of last 20 tickets = 20 * 20 = 400 revenue generated from sales of 50 tickets = 120 + 340 + 400 = 860 $ answer c"
Answer: C