Given a math problem with context and a question and 5 answer choices, the task is to provide the correct answer choice based on the problem. You must choose one of the given answer choices by letter: a, b, c, d, or e; anything else is invalid.
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Question: Problem: a merchant sells an item at a 20 % discount, but still makes a gross profit of 20 percent of the cost. what percent of the cost would the gross profit on the item have been if it had been sold without the discount ?
Options: a. 20 %, b. 40 %, c. 50 %, d. 60 %, e. 75 %

Answer: c


Question: Problem: if the average ( arithmetic mean ) of a and b is 45 and the average of b and c is 80, what is the value of c − a ?
Options: a. 25, b. 60, c. 90, d. 140, e. it can not be determined from the information given.

Answer: b


Question: Problem: if henry were to add 9 gallons of water to a tank that is already 3 / 4 full of water, the tank would be 7 / 8 full. how many gallons of water would the tank hold if it were full ?
Options: a. 25, b. 40, c. 64, d. 72, e. 96

Answer:
d