A coin is tossed n times the probability of getting head at least once is greater than 0.8 . Then, the least value of such n is :

Step-by-step solution

The probability of getting head = 1 2 . The probability of getting head atleast once in n times. = 1 2 + 1 2^2 + + 1 2^n = 1 2 (1- ( 1 2 )^n ) 1- 1 2 =1- ( 1 2 )^n Given that, 1- ( 1 2 )^n>0.8 ( 1 2 )^n < 0.2 2^n> 1 0.2 2^n>5 least value of n for which 2^n>5 is n=3 .