Expected valuehardFree question
| Prize | Probability |
|---|---|
| £0 | 40% |
| £5 | 35% |
| £25 | 20% |
| £40 | 5% |
A raffle ticket pays the prizes shown with the stated probabilities. What is the expected value of one ticket?
A£5.00
B£18.25
C£8.75
D£70.00
E£17.50
Worked solution
Expected value = Σ(outcome × its probability). The correct answer is £8.75. Traps to avoid: £5.00 comes from the "single best term" error; £18.25 comes from the "misaligned probs" error; £70.00 comes from the "summed values" error; £17.50 comes from the "unweighted mean" error.
The wrong answers here have names
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