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.

Q: Problem: the average of 11 10 prime numbers which are odd is ?
Options: a. 17.72, b. 18.52, c. 19.63, d. 16.53, e. 15.63

A: a
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Q: Problem: the average age of a family of 5 members is 20 years. if the age of the youngest member be 10 years then what was the average age of the family at the time of the birth of the youngest member ?
Options: a. 13.5, b. 14, c. 15, d. 12.5, e. none

A: d
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Q: Problem: for a certain exam, a score of 58 was 2 standard deviations below mean and a score of 98 was 3 standard deviations above mean. what was the standard deviation for the exam ?
Options: a. 7, b. 6, c. 8, d. 0, e. 2

A:
c
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