Coin tosses probability to calculate I'm stuck at solving the following problem: launch 3 fair coins independently. Let A the event: &quot;you get at least a head&quot; and B &quot;you get exactly one tail&quot;.
Then what is the probability of the event $A \cup B$?
The probability that you want is everything except if you get all $3$ tails, since everything else is in the union of $A$ and $B$. So the answer = $1 - \frac{1}{8} = \boxed{\frac{7}{8}}$.
Enumerate all 8 possible outcomes (e.g., HHH, HHT, etc.)
Count how many outcomes satisfy A or B.
Divide by 8.