Learn data science & AI, one step at a time.
Pick your role. Each step is a topic, with its interview questions and answers, a lab or a tool where there is one, and the guide. What you mark stays in this browser, with no sign-up.
Short lessons:Data Analyst (6)Data Scientist (7)How LLMs work (6)
Look it up:the glossarythe formula decoder
The Data Analyst path
Step 1Module 3
Excel
15 interview questions1 lesson
Questions and answersLesson: Charts that answer the question
Step 2Module 4
SQL
57 interview questionsSQL Lab: 40 questions1 lesson
Questions and answersLesson: SQL that answers questionsSQL LabThe SQL guide
Step 3Module 1
Python
38 interview questionsPython Lab: 35 questions
Step 4Module 2
Statistics
27 interview questions2 lessons
Questions and answers2 lessonsA/B test calculatorCentral limit theorem
Step 5Module 3
Power BI
41 interview questions1 lesson
Questions and answersLesson: Power BI’s filter contextThe Power BI guide
Step 6The capstones
Cases and guesstimates
27 interview questions1 lesson
Step 1Module 1
Python
49 interview questionsPython Lab: 35 questions
Step 2Module 2
Statistics
31 interview questions2 lessons
Questions and answers2 lessonsA/B test calculatorCentral limit theorem
Step 3Module 4
SQL
57 interview questionsSQL Lab: 40 questions
Step 4Module 5
Machine learning
70 interview questionsML Lab: 40 questions4 lessons
Questions and answers4 lessonsML LabConfusion matrixOverfittingThe ML guide
Step 5Module 6
Deep learning
34 interview questions1 lesson
Questions and answersLesson: How a neural network learnsNeural network
Step 1Module 1
Python
48 interview questionsPython Lab: 35 questions
Step 2Module 5
Machine learning
70 interview questionsML Lab: 40 questions
Questions and answersML LabConfusion matrixOverfittingThe ML guide
Step 4Modules 7 and 8
LLMs and GenAI
51 interview questions6 lessons
Questions and answers6 lessonsToken counterTemperature playgroundThe GenAI guide
A ring fills as you mark questions “Got it” on the topic’s page, and as you solve its lab’s questions. Kept in this browser only.
Labs and tools, free in your browser.
See them all- SQL Lab40 interview questions on real PostgreSQL, checked as you go.
- Python Lab35 questions in real Python with pandas and NumPy.
- ML Lab40 machine learning questions with real scikit-learn and its charts.
- Interview practiceAnswer 5 questions for your role; Prism shows what you covered and what to add.
- Token counterHow many tokens your text takes on GPT-5, Gemini and Sarvam, in Hindi or English.
- Temperature playgroundMove temperature, top-k and top-p on a real model’s chances.
- RAG chunkingCut a real document and see what a search by meaning and by keywords finds.
- Confusion matrixMove a real churn model’s line and watch precision, recall and the ROC curve.
- OverfittingFit a curve of degree 0 to 15 and watch its error on new points fall, then soar.
- A/B test calculatorHow many visitors a test needs, whether a result is significant, and why peeking misleads.
- Central limit theoremWatch averages of any shape turn into a bell, and what 95% confidence means.
- Neural networkTrain a small network on XOR, a circle or a spiral, and watch it learn.