Probability 4 Question 26
26. A lot contains 20 articles. The probability that the lot contains exactly 2 defective articles is 0.4 and the probability that the lot contains exactly 3 defective articles is 0.6 . Articles are drawn from the lot at random one by one without replacement and are tested till all defective articles are found. What is the probability that the testing procedure ends at the twelfth testing?
Show Answer
Solution:
- The testing procedure may terminate at the twelfth testing in two mutually exclusive ways.
I : When lot contains 2 defective articles.
II : When lot contains 3 defective articles.
Let
Here,
