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Question
A box contains 100 bulbs, 20 of which are defective. 10 bulbs are selected for inspection. Find the probability that none is defective
Solution
Out of 100 bulbs, 10 can be chosen in 100C10 ways.
So, total number of elementary events = 100C10
'None is defective' means that all are non-defective bulbs. The number of ways of selecting all 10 non-defective bulbs out
of 80 is 80C10 ways.
∴ Favourable number of elementary events = 80C10
Hence, required probability = \[\frac{^{80}{}{C}_{10}}{^{100}{}{C}_{10}}\]
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