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Updated weekly · Last refresh Aug 30

Cobblestone Energy Data Scientist Interview Questions

The questions to prepare for a Cobblestone Energy Data Scientist interview. Questions from real interview reports rank first. Updated weekly.

28questions
~4htotal time
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1
Statistics & ProbabilityStart here. 11 questions · ~97 min
Two Dice Sum Above EightEasy

Compute the probability that the sum of two fair dice is greater than 8 by counting favorable outcomes.

DistributionsExpected ValueConditional ProbabilityCobblestone Energy
Simple Decimal DivisionEasy

Compute a basic decimal division and interpret what the quotient means.

mental matharithmeticdivisionCobblestone Energy
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2
A/B Testing & Experimentation3 questions · ~27 min
A/B Test for Trading WorkflowMedium

Design an experiment for a new trading signal or workflow change, including metrics, power, randomization, and launch criteria.

experiment designGuardrail Metricsprimary metricsCobblestone Energy
Plan Sample Size for In-App ExperimentMedium

Estimate sample size and power for an experiment, define MDE and guardrails, and decide whether the test is worth running.

MDEPower AnalysisSample SizeCobblestone Energy
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3
Behavioral & Leadership8 questions · ~71 min
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4
More topics6 questions · ~53 min
SQL Window Functions for Market TrendsMedium

Tests practical SQL skills for time-series feature engineering and market ranking.

Window FunctionsLag/LeadRankingCobblestone Energy
UK Wind Drop and Spark SpreadsHard

Tests energy market intuition and ability to connect generation shifts to trading-relevant margins.

market dynamicsCobblestone Energy
Diagnosing Metric DropsHard

Tests debugging, root-cause analysis, and separation of data quality problems from true signals.

Data QualityKPIDiagnosisCobblestone Energy
Peak Demand Prediction ModelMedium

Tests ability to design and justify an ML approach for forecasting energy demand patterns.

Feature EngineeringSupervised LearningTime SeriesCobblestone Energy
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Hands-on SQL practiceWrite and run real queries in the editor. 3 drills · ~30 min
Second Highest Trader SalaryEasy
Practice
Practice drill

Find the second highest distinct salary from a single table using basic PostgreSQL ordering and limiting.

SubqueriesRankingSortingeClinicalWorksInformaticaSpectraforce Technologies
Window Functions for Salary TrendsMedium
Practice
Practice drill

Rank Paylocity employees by department and calculate salary changes between consecutive quarters using RANK and LAG.

Window FunctionsLag/LeadRankingPaylocity
SQL Latest Passing Run Before Each FailureHard
Practice
Practice drill

Use a self-join and PostgreSQL DISTINCT ON to find the latest matching pass before each failed Apex QA test run.

Window FunctionsLag/LeadRankingApex Systems
The finish line: interview-readyComplete all 28 questions plus 3 hands-on drills to finish this plan.