Calculate variance for coin flips
Last updated: January 9, 2026
Quick Overview
Given the following scenario about revenue per session, calculate the the sample size needed.
Snapchat
January 9, 20267
5
576 solved
Given the following scenario about revenue per session, calculate the the sample size needed.
This statistics question from Snapchat's Phone Screen tests your ability to apply mathematical reasoning to practical problems. The interviewer expects precise definitions, correct methodology, and awareness of assumptions and limitations.
What the Interviewer Expects
- Set up the problem formally with proper notation
- Apply the correct statistical test with clear justification
- Interpret results with appropriate caveats and confidence levels
- Discuss practical significance vs statistical significance
- Identify potential confounders and how to address them
Key Topics to Cover
How to Approach This
- Define your hypotheses (H0 and H1) clearly before performing any test.
- Calculate required sample size BEFORE running an experiment, using power analysis.
- Remember the Central Limit Theorem: sample means become approximately normal with large n.
- Watch for Simpson's paradox. Always segment data by key dimensions.
- Distinguish between statistical significance and practical significance.
Possible Follow-up Questions
- What alternative statistical method could you use here?
- What assumptions does this test make, and how would you validate them?
- How would you handle multiple comparisons?
- How would you explain this result to a non-technical audience?
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Problem Formulation
To determine the sample size needed to estimate the average revenue per session from coin flips, we need to set up a framework using the concepts of variance and confidence intervals. Let's denote:
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Solution Approach
- Determine the variance: Let's assume prior data suggests that the variance of revenue per session is $25 (this is an example value).
- Decide on the confidence level: For a ...
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