Proportion of moviegoers who buy popcorn = p = 40% = 0.40
Total number of people = n = 80
The expected number of people who will buy popcorn will be equal to the product of the proportion p and the total number of people n.
So,
Expected Number of buyers = np
= 0.40 x 80
= 32
Thus, from 80 moviegoers we would expected 32 of them to buy popcorn.