Question

When the health department tested private wells in a county for two impurities commonly found in drinking water, it found that 10% of the wells had neither impurity, 80% had impurity A, and 30% had impurity B. (Obviously, some had both impurities.) If a well is randomly chosen from those in the county, find the probability distribution for Y, the number of impurities found in the well.

Answer 1

Answer:

It's because

P(Y=1)=P[(A∩B)∪(A∩B)]

=(.4−.1)+(.5−.1)

=.3+.4

=.7