Answer:
Expected number of visits to the emergency room that would require a surgery is 336.
Step-by-step explanation:
Let <em>X</em> = number of surgery.
The odds of having a surgery in a randomly selected visit to a emergency room is 4 out of 10.
Then the probability of having a surgery in a randomly selected visit to a emergency room is:

In the past month a large urban hospital had 840 emergency visits.
An emergency room visit may lead to surgery or not is independent of the others.
The random variable <em>X</em> follows a Binomial distribution with parameters <em>n</em> = 840 and <em>p</em> = 0.40.
The expected value of a binomial random variable is:

Compute the expected number of visits that would require a surgery as follows:


Thus, expected number of visits to the emergency room that would require a surgery is 336.