Life Span of a Television Part The life (in months) of a
certain television part has a probability density function
defined by
$f(t)=\frac{1}{3} e^{-t / 3}$
Find the probability that a randomly selected component will last for the following lengths of time.
(a) At most 9 months
(b) Between 3 and 9 months
(c) Find the cumulative distribution function for this random variable.
(d) Use the answer from part (c) to find the probability that a randomly selected part will last no more than 6 months.