Problem-Solving and Data AnalysisVery hardConditional probability from a two-way table
Problem-Solving and Data Analysis practice question
The table summarises 120 adults by whether they own a bicycle and whether they own a car. | Owns a car | No car | Total Owns a bicycle | 30 | 20 | 50 No bicycle | 40 | 30 | 70 Total | 70 | 50 | 120 If one of the adults who owns a car is chosen at random, what is the probability that the adult also owns a bicycle?
Answer: 3/7
Restrict to the 70 car owners; 30 of them own a bicycle. 30/70 = 3/7.
Common wrong answers
- If you answered 1/4
- 1/4 is 30/120, the probability over all adults, not among car owners.
- If you answered 3/5
- 3/5 is 30/50, the probability a bicycle owner owns a car (the condition reversed).
- If you answered 7/12
- 7/12 is 70/120, the probability of owning a car at all.
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