Question: After measuring the duration of many telephone calls, the telephone company found their data was well approximated by the density function p(x) = 0.4e-0.4x, where x is the duration of a call, in minutes.
(a) What percentage of calls last between 1 and 2 minutes?
(b) What percentage of calls last 1 minute or less?
(c) What percentage of calls last 3 minutes or more?
(d) Find the cumulative distribution function.