Question

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? 3/190 or 0.01579 3/20 or 0.15 ¼ or 0.25 3/17 or 0.176

Answer 1

3/190 or 0.01579

Explanation:

Probability is generally expressed as a fraction where the numerator is the number of desired outcomes and the denominator is the total number of outcomes. In this case, the desired outcome, or the one being measured, is how many defective toothbrushes are sold. Since there are 20 total toothbrushes and three are defective, the probability of selecting one is:

`(3)/(20)`

Since you are selecting two, you need to multiply the probability of selecting one and then the other:

`(3)/(20)*(2)/(19)=(6)/(180)=(3)/(190)=0.01579`

The probability of getting a defective toothbrush the first time is 3/20, however, since one is sold there would only be two defective toothbrushes left and 19 total. Multiplying these two probabilities together gives you the overall probability that the first two toothbrushes sold are defective.