Step-by-step explanation:
since Poisson distribution parameter is not given so we have to estimate it from the sample data. The average number of of arrivals per minute at an ATM is

So probabaility for
is

So expected frequency for
is
(or
.
Remember distributive property
a(b+c)=ab+ac
we can ervers it
6(31)+6(4)-6(15)=6(31)+6(4)+6(-15)=6(31+4-15)=6(20)=120
Answer:

Step-by-step explanation:
