On a Saturday night, each of the rooms at a certain motel was rented for either $40 or $60. If 10 of the rooms that were rented for $60 had instead been rented for $40, then the total rent the motel charged for that night would have been reduced by 50 percent. What was the total rent the motel actually charged for that night ?  Pick one.
A) $ 400  B) $ 800  C) $ 1,000  D) $ 1,600  E) $ 2,400

Rationale: "let total rent the motel charge for all rooms = x if 10 rooms that were rented for 60 $ had instead been rented for 40 $ , then total difference in prices = 20 $ * 10 = 200 $ total rent the motel charged would have been reduced by 50 % . 5 x = 200 = > x = 400 answer a"
Answer: A