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In a box containing 100 bulbs, 10 are defective. The probability that out of 20 bulbs selected at random, none is defective is
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The correct answer is:
$\left(\frac{9}{10}\right)^{20}$
Let $\mathrm{X}$ denote number of defective bulbs out of 20 bulbs $\mathrm{p}=$ probability of getting defective bulb $=\frac{10}{100}=\frac{1}{10}$ $\therefore \mathrm{q}=1-\frac{1}{10}=\frac{9}{10}$ and $\mathrm{n}=20$, Probability of getting no detective bulb is $={ }^{20} \mathrm{C}_{0}\left(\frac{9}{10}\right)^{20}\left(\frac{1}{10}\right)^{0}=\left(\frac{9}{10}\right)^{20}$
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