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 mean of 50 observations is 200. but later he found that there is decrements of 34 from each observations. what is the the updated mean is ?
Options: a. 165, b. 166, c. 190, d. 198, e. 199
[A]: b


[Q]: Problem: 45 workers work 8 hours to dig a hole 30 meters deep. how many extra workers should be hired to dig another hole 55 meters deep by working for 6 hours ?
Options: a. 50, b. 55, c. 60, d. 65, e. 70
[A]:
d