Question

An unbiased coin is tossed an infinite number of times. The probability that the fourth head appears at the tenth toss is

• A. 0.067
• B. 0.073
• C. 0.082
• D. 0.091

Answer 1

The correct option is C 0.082

$p=\frac{1}{2},q=\frac{1}{2}$

Required probability $={}^9{C}_3{\left(\frac{1}{2}\right)}^3{\left(\frac{1}{2}\right)}^6\times \frac{1}{2}$

$=\frac{84}{1024}=0.082$