Three defective electric toothbrushes were accidentally shipped to a drugstore by the manufacturer along with 17 non-defective ones. What is the probability that the first two electric toothbrushes sold will be returned to the drugstore because they are defective?
A) 3/20 or 0.15
B) 3/17 or 0.176
C) 1/4 or 0.25
D) 3/190 or 0.01579
E) None of the choices are correct

Question

Quizplus · Accepted Answer

The probability that the first toothbrush sold is defective is 3/20. If the first is defective, the probability that the second is also defective is 2/19. Thus, the probability that both are defective is (3/20) * (2/19) = 6/380 = 3/190.

Three Defective Electric Toothbrushes Were Accidentally Shipped to a Drugstore