# Probability: Probabilty Distributions – #455

Question: The duration of telephone calls in certain city is measured by a random variable $$X$$ with probability density

$f(x)=0.5{{e}^{-0.5x}}$

where $$x$$ denotes the duration in minutes of a randomly selected call

(a) What percentage of the calls can be expected to last between 2 and 3 minutes?

(b) What percentage of the calls can be expected to last 2 minutes or less?

(c) What percentage of the calls can be expected to last more than 2 minutes