numeric
Is 550 heads in 1,000 flips suspicious?
Statistics & Inference · Intervals & Errors · medium · Reported at D. E. Shaw · 10 min
A coin is flipped 1,000 times and lands heads 550 times. Under the null hypothesis that the coin is fair, use the normal approximation without continuity correction. What is the z-score for the observed number of heads? Round to two decimals.
Answer as a number of standard deviations, for example 2.50.
Evaluation criteria
- Uses null standard deviation sqrt(np(1-p)) = sqrt(250)
- Computes (550 - 500) / sqrt(250)
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Source
Adapted from a reported D. E. Shaw interview question on DataLemur(opens in a new tab).
Your answer
standard deviations
Commas, currency symbols and a trailing percent sign are fine. Answers within ±0.05 standard deviations of the expected value are accepted.
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