A supplier delivers an order for 20 electric toothbrushes to a store. By accident, three of the electric toothbrushes are defective. What is the probability that the first two electric toothbrushes sold will be returned because they are defective?
A) 3/20 or 0.15
B) 3/17 or 0.176
C) ¼ or 0.25
D) 3/190 or 0.01579

Question

Quizplus · Accepted Answer

The probability of the first toothbrush being defective is 3/20. After the first toothbrush is sold, there are now 19 toothbrushes left, and 2 of them are defective. Therefore, the probability of the second toothbrush being defective is 2/19.

The probability of both events happening (selling two defective toothbrushes in a row) is the product of their independent probabilities:

3/20 * 2/19 = 6/380 = 3/190 or 0.01579

Therefore, the answer is D.

A Supplier Delivers an Order for 20 Electric Toothbrushes to a Store