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 probability of two events a and b are 0.25 and 0.40 respectively. the probability that both a and b occur is 0.15. the probability that neither a nor b occur is _________
Options: a. 0.45, b. 0.4, c. 0.5, d. 0.05, e. 0.6
[A]: c


[Q]: Problem: the speed of the boat in still water in 12 kmph. it can travel downstream through 54 kms in 3 hrs. in what time would it cover the same distance upstream ?
Options: a. 8 hours, b. 6 hours, c. 4 hours, d. 5 hours, e. 9 hours
[A]: e


[Q]: Problem: a train passes a station platform in 36 sec and a man standing on the platform in 20 sec. if the speed of the train is 54 km / hr. what is the length of the platform ?
Options: a. 120 m, b. 240 m, c. 300 m, d. 500 m, e. 550 m
[A]:
b