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  4. An unbiased coin is tossed eight times. The probability of obtaining at least one head and at least one tail is :

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Q. An unbiased coin is tossed eight times. The probability of obtaining at least one head and at least one tail is :

JEE MainJEE Main 2017Probability - Part 2

Solution:

1 - $\int$ P(All Head) + P(AllTail)
$1 - \left\{\frac{1}{2^{8}}+\frac{1}{2^{8}}\right\}$
$= 1-\frac{1}{2^{7}}$
$= 1-\frac{1}{128} = \frac{127}{128}$