A biotechnology company produced 189 doses of somatropin, including 11 which were defective. Quality control test 13 samples at random, and rejects the batch if any of the random samples are found defective. What is the probability that the batch gets rejected?

Question

anonymous · Answer

The first sample has odds of 11/189 of being defective.  The second sample will have 11/188 odds of being defective because on the second sampling there are 188 samples left.  On the third there will be 187 etc.
$$\sum_{n=1}^{13}11/(189-n)$$

anonymous · Answer

84.42%