instruction:
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.
question:
Problem: in what time will a train 120 m long cross an electric pole, it its speed be 121 km / hr ?
Options: a. 2.5, b. 2.7, c. 2.9, d. 3.6, e. 2.1
answer:
d

question:
Problem: the first flight out of phoenix airport had a late departure. if the next 3 flights departed on - time, how many subsequent flights need to depart from phoenix on - time, for the airport ' s on - time departure rate to be higher than 40 % ?
Options: a. 4, b. 6, c. 5, d. 2, e. 8
answer:
d

question:
Problem: a certain list consists of 21 different numbers. if n is in the list and n is 5 times the average ( arithmetic mean ) of the other 20 numbers in the list, then n is what fraction of the sum of the 21 numbers in the list ?
Options: a. 1 / 20, b. 1 / 6, c. 1 / 5, d. 4 / 21, e. 5 / 21
answer:
c