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: 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
[EX A]: a

[EX Q]: Problem: the l. c. m of two numbers is 495 and their h. c. f is 5. if the sum of the numbers is 100, then their difference is
Options: a. 19, b. 10, c. 28, d. 27, e. 29
[EX A]: b

[EX Q]: Problem: a cat chases a rat 6 hours after the rat runs. cat takes 4 hours to reach the rat. if the average speed of the cat is 90 kmph, what s the average speed of the rat ?
Options: a. 32 kmph, b. 26 kmph, c. 35 kmph, d. 36 kmph, e. 32 kmph
[EX A]:
d