Four unbiased coins are tossed. What is the probability of getting atmost three heads?

To find the probability of getting at most three heads, we will use the complement rule (P(not A)

At most three heads means we can get 0, 1, 2, or 3 heads.

The complement of this event is getting exactly 4 heads.

Since four unbiased coins are tossed, the total number of possible outcomes is:

2^4 = 16

The only way to get 4 heads is HHHH, which is 1 outcome.

P(exactly 4 heads)=1/16

P(at most 3 heads)=1−P(exactly 4 heads)

=1−1/16 = 15/16