Three unbiased coins are tossed. What is the probability of getting at least 2 heads?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → \(\frac{1}{2}\)
Each coin can fall in 2 ways, so three coins give \(2\times2\times2=8\) equally likely outcomes. “At least 2 heads” means 2 heads or 3 heads.
Outcomes with at least 2 heads: HHT, HTH, THH, HHH, that is, 4 outcomes
Probability \(\displaystyle =\frac{4}{8}=\frac{1}{2}\)
Shortcut: Heads and tails are equally likely, so the two cases below have the same probability:
Every throw of three coins gives either at least 2 heads or at least 2 tails, never both
So each has probability \(\frac{1}{2}\)