Question

the computer that controls a banks automatic teller machine crashes a mean of 0.4 times per day. what is the probability that in any seven day week the computer will crash more than 5 times

Answer 1

We are given, mean = 0.4 times per day.

We have to find weekly probability.

So, Weekly mean = 0.4*7 = 2.8

We need to use Poisson distribution with mean = 2.8

We have to find P( x > 5 )

P( x > 5 ) = 1 - P( x <= 5 )

Using Excel function ,   =POISSON.DIST( x , mean , 1 )

P( x <= 5 ) = POISSON.DIST( 5 , 2.8 , 1 ) = 0.93489

So, P( x > 5 ) = 1 - 0.93489 = 0.06511

Answer: The probability that, in any 7-day week, the computer will crash more than 5 time is 0.06511