#### 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.

\[\text{ Here } , p = q = \frac{1}{2}\]

\[P(X = \text{ odd} ) = P(X = 1, 3, 5, . . . . 99) \]

\[ = \left( ^{100}{}{C}_1 + ^{100}{}{C}_3 + . . . . . + ^{100}{}{C}_{99} \right) \left( \frac{1}{2} \right)^{100} \]

\[ = \text{ Sum of odd coefficients in binomial expansion in}\ (1 + x )^{100} \left( \frac{1}{2} \right)^{100} \]

\[ = \frac{2^{(100 - 1)}}{2^{100}}\]

\[ = \frac{1}{2}\]

Is there an error in this question or solution?

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.