Problem-Solving and Data AnalysisVery hardProbability of a particular sum on two spins
Problem-Solving and Data Analysis practice question
A spinner has 8 equal sections numbered 1 to 8. It is spun twice. What is the probability that the two numbers add up to 3?
Answer: 1/32
There are 64 equally likely pairs. Only (1, 2) and (2, 1) add to 3: 2/64 = 1/32.
Common wrong answers
- If you answered 1/64
- 1/64 counts only one of the two orders.
- If you answered 1/16
- 1/16 counts four pairs, wrongly including (3, 0) or repeats.
- If you answered 3/64
- 3/64 counts three pairs, but 0 is not on the spinner.
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