If you toss a fair coin and the probability of heads is 1/2, what is the probability of NOT getting heads?
A0
B1/4
C1/2
D1
Answer & Solution
Correct answer: C. 1/2
For any event A: P(A) + P(not A) = 1 (the sum of all probabilities equals 1). So P(not heads) = 1 − 1/2 = 1/2. (Equivalently, P(tails) = 1/2 — same thing for a 2-outcome experiment.) This is the 'complement rule'.
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