#The exponiential distribution models the waiting time between events that occur randomly and independently.\
#Such events are said to occur according to Poisson process.

#rexp(n, lamda)generates n random values from the exponiential distribution with mean lamda
rexp(4,2)

#pexp(x,lamda) is the CDF.
pexp(c(.25,.50,.75,1.00),2)

#qexp(p,lamda) is the inverse distribution function.It returns the value x such that pexp(x,lamda)=p.
qexp(c(.20,.40,.60,.80),2)

#dexp(x,lamda) is the PDF.

#Example. Calls to a customer service line come at an average rate of 6 every 5 minutes.
#1. what is the probability that at least 3 minutes elapse without a call?
1-pexp(3,6/5)

#2.What is the 95th percentile for time between calls?
qexp(.95,6/5)