Discussion
Three unbiased coins are tossed. What is the probability of getting at most two heads?
Answer: D
"At most two heads" means everything except three heads, so use the complement.
\[ P(\text{3 heads}) = \frac{1}{8} \]
\[ P(\text{at most 2}) = 1 - \frac{1}{8} = \frac{7}{8} \]
Counting zero, one and two heads directly gives \( 1 + 3 + 3 = 7 \) of the 8 outcomes - the same answer for more work.
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