Look up the formula for the individual terms of a Binomial Distribution.
You have p = 0.8, q = 1-p = 0.2, and n = 20.
The probability that a patient recovers from a stomach disease is .8. Suppose 20 people are known to have contracted this disease.
Let X = # of people who recover out of 20 contracted the disease
while PMF for X and solve problems. Assume that sample of size 20 is independently selected.
A. What is the probability that exactly 14 recover?
B. What is the probability that at least 10 recover?
C. What is the probability that at least 14 but not more than 18 recover?
D. What is the probability that at most 16 recover?