Three unbiased coins are tossed. What is the probability of getting at most two heads?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 7/8
Three coins give \(2^{3}=8\) equally likely outcomes. “At most two heads” means 0, 1 or 2 heads, which is every outcome except three heads, so it is quicker to subtract the one outcome HHH from the whole.
Probability of three heads (HHH only): \(\displaystyle\frac{1}{8}\)
Probability of at most two heads: \(\displaystyle1-\frac{1}{8}=\frac{7}{8}\)