Waiting time follows an exponential distribution with mean
μ=60
μ=60 seconds. This implies λ=1μ=160λ= μ1= 601
Let X be the waiting time. for first we have to calculate the probability of customers who wait less than 30 secs.
a. X is less than 30 seconds, then we have to find ,
P(X<X1)=1−e−λX1⇒P(X<30)=1−e−λ×0
=1−e−160×30 =1−e−12=1−0.6065
=0.3935P(X<X 1)⇒
P(X<30)
=1−e −λX 1=
1−e −λ×30 1−e − 601×30 =
1−e − 21
=1−0.6065
=0.3935
b. X is more than 120 seconds, then we have to find less than 120 sec
b. X is more than 120 seconds
P(X>X1)=1−P(X<X1)=1−(1−e−λX1)⇒P(X>120)=1−(1−e−λ×120=e−60×120=e−2=0.135
P(X>X 1)⇒P(X>120)=1−P(X<X 1)=1−(1−e −λX 1)=1−(1−e −λ×120= − 601×120 =e −2=0.135
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