Question

9 defective electric toothbrushes were accidentally shipped to a drugstore by Cleanbrush Products along with 29 nondefective ones.

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

Answer 1

Let $D$ denote the event "electric toothbrush is defective".

$$P(D^CD^C)=\dfrac{29}{9+29}(\dfrac{28}{9+28})=\dfrac{406}{703}\approx0.5775$$