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 shopkeeper sold 30 articles at the cost price of 35 articles. then find the profit % or lost %
Options: a. 12 %, b. 15 %, c. 16.67 %, d. 18 %, e. 22 %

Answer: c

Question: Problem: the present population of a town is 2000. population increase rate is 20 % p. a. find the population of town after 1 years ?
Options: a. 1000, b. 2400, c. 1500, d. 1600, e. 1250

Answer: b

Question: Problem: i sold a book at a profit of 10 %. had i sold it for $ 110 more, 15 % would have been gained. find the cost price ?
Options: a. $ 2000, b. $ 2200, c. $ 3000, d. $ 3120, e. $ 1540

Answer:
b