How many times must a person toss a coin if the chances of obtaining at least one head are 91% or better?
A) 4 times
B) 35 times
C) 3 times
D) 6 times

Question

How many times must a person toss a coin if the chances of obtaining at least one head are 91% or better? ​
A) 4 times
B) 35 times
C) 3 times
D) 6 times

Quizplus · Accepted Answer

The probability of getting a head on a single coin toss is 1/2. The probability of not getting a head is also 1/2. The probability of not getting a head in n tosses is (1/2)^n. The probability of getting at least one head in n tosses is 1 - (1/2)^n. We want to find the smallest n such that 1 - (1/2)^n >= 0.91. Solving for n, we get n >= 4.

How Many Times Must a Person Toss a Coin If