Statistical Inference vs Quarry

Statistical Inference is an independent study app built for students, self-learners, analysts, and anyone reviewing core inference ideas through focused practice. Work through 160 questions across Fundamentals, Practical Skills, Common Pitfalls, and Advanced Concepts. Each question includes an explanation so you can understand why an answer works, not just whether you got it right. Features: - FSRS spaced-repetition intervals to help reviews land at the right time - Weak-point heatmap to show where you need more practice - Daily challenge for consistent study - Mock exams for timed review - Offline practice for commutes, classrooms, and low-signal moments - No login required Use it to review estimation, confidence intervals, hypothesis testing, p-values, sampling distributions, power, errors, likelihood ideas, and common interpretation traps. Practice offline, no login required. Independent study app for Statistical Inference practice. Not affiliated with, endorsed by, or sponsored by any company, certification body, exam operator, or vendor. All trademarks belong to their respective owners.

Data interview practice that runs entirely on your device. Write real SQL and Python (pandas), get graded instantly, and see exactly why. NEW IN 1.1 • Designed for iPhone Duo: question and editor side by side when open, a focused layout when closed, and it adapts as you fold. • A new native design for iPhone and iPad, in light and dark mode. • 60 new problems: a staff-level data engineering set (gaps and islands, sessionisation, slowly changing dimensions, funnels, retention) and company-style SQL sets. • Clearer results: instant correct / not quite feedback, expected vs. actual tables, and the query plan for your SQL. WHAT'S INSIDE • 168 problems across three tracks: 61 SQL, 22 pandas and 85 Python (algorithms and data structures). • Real execution, real grading. Your output is checked against the expected result, with no self-marking. • Company-style practice. Filter problems written in the style of the company you're interviewing at. • Hints and full solutions when you're stuck. • Difficulty levels from Easy to Hard, grouped by topic. • A free-form Playground for scratch SQL and Python. PRIVATE BY DESIGN No accounts. No analytics. No ads. No tracking. Quarry collects nothing and works fully offline. Built by a working data engineer, for analysts, data engineers, data scientists and software engineers who want a quiet, fast place to actually practice.