Question

A box has 20 pens of which 2 are defective. calculate the probability that out of 5 pens drawn one by one with replacement, at most 2 are defective.

Answer 1

The probability of getting a defective pen from the box is 2/20=1/10

Out of the five pens the probability of getting at most 2 defective pens is

1/5 or 2/5

The probability of getting a defective pen from the five picked is thus:

(1/5+2/5) ×1/10=3/5×1/10=3/50

3/50