A retailer determines that the average number of orders per

A retailer determines that the average number of orders per day for a
certain product is 5. Assume the Poisson distribution is applicable.
What is the probability that at least 2 order is received on a given day?

.0023

.9596

.9210

.0000

none of the above

Solution

Note that P(at least x) = 1 - P(at most x - 1).          
          
Using a cumulative poisson distribution table or technology, matching          
          
u = the mean number of successes =    5      
          
x = our critical value of successes =    2      
          
Then the cumulative probability of P(at most x - 1) from a table/technology is          
          
P(at most   1   ) =    0.040427682
          
Thus, the probability of at least   2   successes is  
          
P(at least   2   ) =    0.959572318 [ANSWER, OPTION B]