Common Core: S-IC.2
Problem 20 of 45s12-020
A coin gave 15 heads in 20 flips. In 100 simulated runs of 20 fair flips, 15 heads came up 3 times, 16 heads twice, 17 once, and more never. With a 5% cutoff, is 15 heads surprising?
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The walkthrough opens once you check an answer.
Solution walkthrough1:43
- The model is a fair coin. Each dot is one simulated run of 20 fair flips, placed at its number of heads.
- Mark the real result, 15 heads, on the plot. Fair runs pile up around 10 heads.
- Count runs at least as extreme as 15: runs, so out of , or .
- is not below the cutoff, so 15 heads is not surprising for a fair coin.
- Traps: count 15 or more, not exactly 15; distance from 10 alone is no test; and not surprising is not proof.