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 4 and 5 minutes? (nearest tenth)

b)What percentage of calls last 4 minutes or less? (nearest tenth)

c)What percentage of calls last 4 minutes or more? (nearest tenth)

d)Express the cumulative distribution function in the form P(x) = { x<0

x greater than or equal to 0