The probability that both parts are defective is 6/55
Explanation:
Defective parts = 4
Total parts = 11
Probability of getting a defective part = 4/11
Probability of getting defective part 2nd time = 3/10
Total probability of getting defective part both the times = (4/11) (3/10)
= (12/110)
= (6/55)
The probability that both parts are defective is 6/55