Answer:
There is a 23.81% probability that fewer than three babies with middle-ear infections will come to her clinic tomorrow.
Explanation:
In a Poisson distribution, the probability that X represents the number of successes of a random variable is given by the following formula:

In which
x is the number of sucesses
e = 2.71828 is the Euler number
is the mean in the given interval.
In this problem
Elizabeth is a busy pediatrician. On any given day, she diagnoses an average of four babies with middle-ear infections. This means that
.
Calculate the probability that fewer than three babies with middle-ear infections will come to her clinic tomorrow.
So





So

There is a 23.81% probability that fewer than three babies with middle-ear infections will come to her clinic tomorrow.