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# A Fair Coin is Tossed 100 Times. the Probability of Getting Tails an Odd Number of Times is (A) 1/2 (B) 1/8 (C) 3/8 (D) None of These - Mathematics

ConceptBernoulli Trials and Binomial Distribution

#### Question

A fair coin is tossed 100 times. The probability of getting tails an odd number of times is

• 1/2

• 1/8

• 3/8

• None of these

#### Solution

1/2
Here n=100
Let X denote the number of times a tail is obtained.

$\text{ Here } , p = q = \frac{1}{2}$
$P(X = \text{ odd} ) = P(X = 1, 3, 5, . . . . 99)$
$= \left( ^{100}{}{C}_1 + ^{100}{}{C}_3 + . . . . . + ^{100}{}{C}_{99} \right) \left( \frac{1}{2} \right)^{100}$
$= \text{ Sum of odd coefficients in binomial expansion in}\ (1 + x )^{100} \left( \frac{1}{2} \right)^{100}$
$= \frac{2^{(100 - 1)}}{2^{100}}$
$= \frac{1}{2}$

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Solution A Fair Coin is Tossed 100 Times. the Probability of Getting Tails an Odd Number of Times is (A) 1/2 (B) 1/8 (C) 3/8 (D) None of These Concept: Bernoulli Trials and Binomial Distribution.
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