15%
of the people in a population have been exposed to a new strain of the
flu. We randomly sample three people
from this population (assume these three people are independent). Find the probability that: all, at least 1, and 2 were exposed.

The probability of an event is the measure of the chance that the event will occur as a result of an experiment. The probability of an event A is the number of ways event A can occur divided by the total number of possible outcomes.

Probability of an event happening =
Number of ways it can happen / Total number of outcomes

so now for the working

sample size = 3

probability that all are exposed=
Number of ways it can happen / Total number of outcomes

probability that all are exposed= 3/3=1 ans

probability that 1 is exposed=
Number of ways it can happen / Total number of outcomes

probability that all are exposed= 1/3= .33 or 33%ans

probability that 2 are exposed=
Number of ways it can happen / Total number of outcomes

probability that all are exposed= 2/3= .66 or 66%ans