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Three defective electric toothbrushes probability problem

Three defective electric toothbrushes were accidentally shipped to a drugstore by Cleanbrush Products along with 17 nondefective ones.

a.) What is the probability the first two electric toothbrushes sold will be returned to the drugstore because they are defective?

b.) What is the probability the first two electric toothbrushes sold will not be defective?

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Hello!
a) Before the first unit is sold, there are 3 units among 18 that are defective. Therefore, there is a 3/18 (=0.1666) probability that the first toothbrush will be defective.

Once the first defective toothbrush has been sold, there are 2 ...

Solution Summary

In this solution, explanation is provided along with a calculation of probability, and an Excel file is attached.

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