The length of a particular telemarketing phone call, x, has an exponential distribution with mean equal to 1.5 minutes.
a) Write down the probability density function of random variable x.
b) Calculate the probability that the length of a randomly selected call will be no more than three minutes.
c) Calculate the probability that the length of a randomly selected call will be between one and two minutes.
d) Calculate the probability that the length of a randomly selected call will be more than four minutes.