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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
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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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