Probability

To solve this problem, we use poisson distribution.
The Poisson probability formula is P(X=k)=‌

λke−λ

k!

Here,
λ=‌ average number of events ‌=4
K= number of events (customer)
So, probability that more than 2 customers visit the shop in a specific hour =P(X>2)
‌=1−P(X≤2)=1−[P(X=0)+P(X=1)+P(X=2)]
‌=1−[‌

40e−4

0!

+‌

41e−4

1!

+‌

42e−4

2!

]=1−[e−4+4e−4+8e−4]
‌=1−13e−4=1−‌

13

e4

=‌

e4−13

e4