Question

How many times must a man toss a fair coin so that the probability of having at least one head is more than 90%?

Answer 1

Let the man toss the coin n times. The n tosses are n Bernoulli trials.

Probability (p) of getting a head at the toss of a coin is `1/2`

It is given that,

P (getting at least one head) > `90/100`

P (x ≥ 1) > 0.9

⇒ 1 − P (x = 0) > 0.9

The minimum value of n that satisfies the given inequality is 4.

Thus, the man should toss the coin 4 or more than 4 times.