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There are N = ways to select 4 CDs from the set of 5000 CDs without replacement.
It is the whole space of samples in this problem.
Next, from the condition, every 4 CDs that pass testing, belong to the subset of 5000-100 = 4900 good CDs.
There are n = ways to select 4 CDs from this set of 4900 CDs.
Therefore, the probability under the question is the ratio
= = = 0.922346. ANSWER
Another way to solve the problem is to use the formula
P =
which is self-explanatory and gives the same result P = 0.922346.
Solved.