Lifetime of an electronic component has an exponential distribution with mean of 100 hours. (Exponential distribution problem)

a. Find the probability that a component operates at least 200 hours.

b. Find the probability that a component operates last 150 and 250 hours.

c. Find the probability that a component operates last less than 100 hours.

d. Find the 99th percentile.

e. What is the standard deviation of X?

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Suppose the lifetimes of a certain brand of televisions are normally distributed with U(MEAN) = 6, Standard deviation = 0.5.

Find the warranty time for the manufacturer so that no more than 1% will have to be replaced. I know the answer is 4.835 but why?