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.

[EX Q]: Problem: the overall age of x and y is 19 year greater than the overall age of y and z. z is how many decades younger that x ?
Options: a. 11, b. 15, c. 12, d. 19, e. 20
[EX A]: d

[EX 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
[EX A]: a

[EX Q]: Problem: 70,76, 74,85, 90,105, 105,130, 130,130 the list consists of the times in seconds that it took each of the 10 school children to run a distance of 400 mts. if the standard deviation of the 10 running times is 22.4, rounded to the nearest tenth of a second, how many of the 10 running times are more than 1 standard deviation below the mean of the 10 running times.
Options: a. 1, b. 2, c. 3, d. 4, e. 5
[EX A]:
c