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 man can row upstream at 25 kmph and downstream at 55 kmph, and then find the speed of the man in still water ?
Options: a. 65, b. 40, c. 30, d. 78, e. 38

Answer: b


Question: Problem: a statue is being carved by a sculptor. the original piece of marble weighed 180 kg. in the first week 28 percent is cut away. in the second week 18 percent of the remainder is cut away. in the third week the statue is completed when 20 percent of the remainder is cut away. what is the weight of the final statue ?
Options: a. 105 kg, b. 85 kg, c. 108 kg, d. 125 kg, e. 117 kg

Answer: b


Question: Problem: if each participant of a chess tournament plays exactly one game with each of the remaining participants, then 153 games will be played during the tournament. find the number of participants.
Options: a. 15, b. 16, c. 17, d. 18, e. 19

Answer:
d