Calculate variance for A/B test results
Last updated: March 20, 2026
Quick Overview
Given the following scenario about revenue per session, calculate the the sample size needed.
Zscaler
March 20, 202610
12
4,863 solved
Given the following scenario about revenue per session, calculate the the sample size needed.
Statistics questions at Zscaler test your ability to reason quantitatively and design rigorous experiments. This Take-home Project question evaluates your understanding of statistical inference and its application to business decisions.
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
- How would you explain this result to a non-technical audience?
- What alternative statistical method could you use here?
- How would you design a follow-up experiment based on these results?
- What assumptions does this test make, and how would you validate them?
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Browse Statistics QuestionsSample Answer
Problem Formulation
To determine the sample size needed for an A/B test evaluating revenue per session, we need to set up the problem using specific statistical notation. Let:
- be the mean revenue per sessio...
Solution Approach
To calculate the required sample size, we use the formula for sample size in a two-sample t-test: [ n = \left\frac{(Z_{\alpha/2} + Z_{\beta})^2 \cdot (\sigma_A^2 + \sigma_B^2)}{d^2} \right \text{ ...
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