Question

What is the probability of all cogs being defective

Answer 1

Prob (first defective) = 4 / 20 = 1/5

Prob(2nd defective) = 3/19

Prob (3rd defective) = 2/18 = 1/9

Pron 4th defective) = 1/ 17

Prob ( all 4 defective) = 1/5 * 3/19 * 1/9 * 1/17 = 1 / 4845 answer