Question

A box contains two defective Christmas tree lights that have been inadvertently mixed with eight nondefective lights. If the lights are selected one at a time without replacement and tested until both defective lights are found, what is the probability that both defective lights will be found after exactly three trials? (Round your answer to four decimal places.)

Answer 1

Possibility 1: nondefective-defective-defective
possibility 2: defective-nondefective-defective

possibility 1: 8/10x 2/9 x 1/8 = 16/720=1/45
possibility 2: 2/10 x 8/9 x 1/8= 16/720=1/45

answer: 2/45