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: if 20 typists can type 50 letters in 30 minutes, then how many letters will 40 typists working at the same rate complete in 1 hour ?
Options: a. 400, b. 500, c. 350, d. 250, e. 200
[A]: a


[Q]: Problem: if the average ( arithmetic mean ) of a and b is 45 and the average of b and c is 80, what is the value of c − a ?
Options: a. 25, b. 60, c. 90, d. 140, e. it can not be determined from the information given.
[A]: b


[Q]: Problem: ravi purchased a refrigerator and a mobile phone for rs. 15000 and rs. 8000 respectively. he sold the refrigerator at a loss of 3 percent and the mobile phone at a profit of 10 percent. overall he make a.
Options: a. 228, b. 350, c. 27, d. 200, e. 881
[A]:
b