A fair die is rolled twice. What is the probability that at least one of the two rolls shows a 4?
Answer
11/36
The correct answer is 11/36 — Hence the required probability is .
Step-by-step solution
- Identify the complementary event: neither roll shows a 4.
- The probability that a single roll is not a 4 is because there are 5 other faces.
- Since the two rolls are independent, the probability that neither roll shows a 4 is .
- The probability of the desired event is the complement: .
- Hence the required probability is .
Common mistake: Adding probabilities of two rolls incorrectly instead of using complement
Concept tested: Complementary event probability with independent trials
Published · How this solution was prepared and checked
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