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All 100 courses, free — 56 build-it · 44 decide-it. Build it in your browser or make the call on a real business scenario; filter to find your next one.

AI & Machine LearningBeat the Baseline: an honest test score, and the dumb model it has to beatAbsBeg 2 · ▶ runs in browser · ~0.5h Part A AI & Machine LearningFeature scaling: why one big-numbered column can wreck a distance-based modelBeg 4 · ~0.75h Part A AI & Machine LearningIs this review positive? Reading sentiment from textBeg 4 · ~0.75h Part A AI & Machine LearningAccuracy is lying to you: evaluating a classifier on imbalanced dataInt 5 · ~1.25h Part A AI & Machine LearningPay Equity: the gap that mostly isn't (raw vs. adjusted)Int 5 · ~1.25h Part A AI & Machine LearningAttrition Leakage: the model that's too good to be trueInt 6 · ~1.25h Part A AI & Machine LearningLead Scoring: a model can rank leads perfectly and still lie about the oddsInt 6 · ~1.0h Part A AI & Machine LearningRecommendations from scratch: matrix factorization that beats the popularity baselineAdv 7 · ~1.5h Part A AI & Machine LearningUplift Targeting: spend on the persuadable, not the sure thingAdv 8 · ~1.5h Part A Data AnalyticsMissing Not at Random: when the blanks aren't an accident, your average liesAbsBeg 1 · ▶ runs in browser · ~0.5h Part A Data AnalyticsAveraging Averages: the company number isn't the mean of the branch numbersAbsBeg 2 · ~0.5h Part A Data AnalyticsOutlier Spotting: one bad reading wrecks the mean, not the medianAbsBeg 2 · ▶ runs in browser · ~0.5h Part A Data AnalyticsPercent-Change Traps: why +20% then -20% doesn't get you backAbsBeg 2 · ▶ runs in browser · ~0.5h Part A Data AnalyticsRounding That Lies: round each line then sum, and the total is wrong by centsAbsBeg 2 · ▶ runs in browser · ~0.5h Part A Data AnalyticsTop-N and the Tail: your best-seller list depends on the metric, and hides most of the moneyAbsBeg 2 · ▶ runs in browser · ~0.5h Part A Data AnalyticsBenford's Law: catching fabricated numbers by their leading digitBeg 3 · ▶ runs in browser · ~0.75h Part A Data AnalyticsCohort Retention: why the topline looks healthy while every cohort leaks worseBeg 3 · ▶ runs in browser · ~1.0h Part A Data AnalyticsDuplicate Invoices: catch the payments that went out twiceBeg 3 · ▶ runs in browser · ~1.0h Part A Data AnalyticsSilent Row Loss: the join that quietly drops (and duplicates) your dataBeg 3 · ▶ runs in browser · ~1.25h Part A Data AnalyticsReading an A/B test: telling a real lift from noiseBeg 4 · ~0.75h Part A Data AnalyticsMaverick Spend: find the purchases that bypassed the contractsBeg 4 · ~1.0h Part A Data AnalyticsPipeline Forecast: weight the deals you have by the deals that actually closeBeg 4 · ~1.0h Part A Data AnalyticsMulti-Touch Attribution: last click lies about who earned the saleInt 5 · ~1.25h Part A Data EngineeringCalendar Gaps: a day with no sale has no row, and it's dragging your average upAbsBeg 1 · ▶ runs in browser · ~0.5h Part A Data EngineeringDate Parsing Basics: a date stored as a string sorts and filters wrongAbsBeg 2 · ▶ runs in browser · ~0.5h Part A Data EngineeringString Key Cleaning: ' Apple ', 'apple', and 'APPLE' are one product, not threeAbsBeg 2 · ▶ runs in browser · ~0.5h Part A Data EngineeringWide to Tidy: melt a spreadsheet report so the next question is one lineAbsBeg 2 · ▶ runs in browser · ~0.5h Part A Data EngineeringCSV to Parquet: store a log columnar and read only the bytes you needBeg 3 · ~1.0h Part A Data EngineeringData contracts: catch the bad rows before they reach your tableBeg 3 · ▶ runs in browser · ~0.75h Part A Data EngineeringIdempotent loads: why re-running your pipeline shouldn't double your dataBeg 3 · ~1.0h Part A Data EngineeringThree-Way Match: pay an invoice only if the order and the receipt agreeBeg 3 · ▶ runs in browser · ~1.0h Part A Data EngineeringSchema Evolution: load a feed that changes its columns out from under youBeg 4 · ~1.0h Part A Data EngineeringVendor Dedupe: one row per real company from a messy supplier masterInt 6 · ~1.25h Part A Finance for ManagersWhere did the money go? Reading a P&L line by lineAbsBeg 2 · ▶ interactive model · ~14 min read Finance for ManagersThe below-list order: what one more unit really earnsBeg 4 · ▶ interactive model · ~16 min read Finance for ManagersIs this project worth it? Payback, NPV, and the discount-rate trapInt 6 · ▶ interactive model · ~19 min read GeospatialSpatial Join: which zone is this point in, really?Beg 3 · ~1.0h Part A GeospatialNearest Facility: distances on a globe, and when the nearest one is fullBeg 4 · ~1.0h Part A GeospatialGeohash Rollup: a base-32 address for the map, that nests and has neighboursInt 5 · ~1.0h Part A GeospatialSpatial Clusters: finding hotspots with DBSCAN, and why k-means can'tInt 5 · ~1.0h Part A GeospatialSpatial Autocorrelation: is the map clustered, and where — Moran's I, global and localInt 6 · ~1.25h Part A GeospatialFacility Location: which depots to open, and why nearest-assignment breaks under capacityAdv 7 · ~1.0h Part A MarketingWhat a customer costs, and how fast you get it backBeg 3 · ▶ interactive model · ~18 min read MarketingSegment or spray? Pointing a limited B2B marketing budgetBeg 3 · ~20 min read MarketingIs this channel working? ROAS, and the margin it hidesBeg 4 · ▶ interactive model · ~16 min read MarketingLTV:CAC — what the ratio really tells you (and what it hides)Beg 4 · ▶ interactive model · ~17 min read MarketingPrice the renewal: how much churn a price rise can affordBeg 4 · ▶ interactive model · ~19 min read MarketingThe last-click trap: who really earned the sale?Int 5 · ~22 min read MarketingBrand or performance? Splitting the budget when the dashboard only sees oneInt 5 · ~23 min read MarketingThe 20%-off trap: when a promo lifts volume and loses moneyInt 5 · ▶ interactive model · ~19 min read MarketingWould it have happened anyway? Incrementality vs attribution in ad spendInt 6 · ~21 min read MarketingOne price, unknown demand: pricing a perishable room block by expected valueAdv 7 · ▶ interactive model · ~24 min read Open-Source LibrariesYour First Test: catch a real bug by testing the boundary, not the happy pathAbsBeg 2 · ▶ runs in browser · ~0.5h Part A Open-Source LibrariesAnalytical SQL with DuckDB: from clickstream to sessionsInt 5 · ~1.0h Part A Open-Source LibrariesHidden communities: finding the groups inside a network and proving they're realInt 5 · ~1.0h Part A Open-Source LibrariesPolars Analytics: window functions for the questions group-by can't answerInt 5 · ~1.0h Part A Open-Source LibrariesFraud Rings: the collusion you can only see in the graphInt 6 · ~1.25h Part A Open-Source LibrariesProperty-Based Testing: let Hypothesis find the input you didn't think ofInt 6 · ~1.5h Part A Open-Source LibrariesWarehouse Sim: find the bottleneck a stopwatch would missInt 6 · ~1.5h Part A Operations & ProcessFind the bottleneck: why the whole line runs at the speed of its slowest stepBeg 3 · ~20 min read Operations & ProcessTriage the queue: what to work next when the backlog is winningBeg 3 · ~21 min read Operations & ProcessLittle's Law in practice: why starting more work makes it slowerBeg 4 · ▶ interactive model · ~17 min read Operations & ProcessMake it or buy it: the unit-economics call, and the volume that flips itInt 5 · ▶ interactive model · ~18 min read Operations & ProcessRunning hot: why an 80%-full clinic waits, and a 95%-full one drownsInt 5 · ▶ interactive model · ~18 min read Operations & ProcessIs the process in control? Common-cause noise vs a real signalInt 6 · ~23 min read People & HRScore the candidate: why a hiring scorecard beats a gut feelingAbsBeg 2 · ~25 min read People & HRThe cost of a bad hire: why structured hiring is cheap insuranceBeg 3 · ▶ interactive model · ~20 min read People & HRAttrition is up 18% — do you have a retention problem? Regretted vs non-regretted attritionBeg 4 · ▶ interactive model · ~22 min read People & HRWho gets the raise? Splitting a fixed merit pool across your teamBeg 4 · ▶ interactive model · ~23 min read People & HRCalibrate the ratings: fair scores between inflation and a forced curveInt 5 · ~25 min read People & HRSet the pay band: fix compression without breaking it for everyoneInt 5 · ▶ interactive model · ~20 min read People & HRManage out, or coach? Deciding when to invest in an underperformer and when to let them goInt 6 · ~25 min read Sales & RevenueA forecast you can defend: commit, best-case, and the number in betweenBeg 3 · ▶ interactive model · ~17 min read Sales & RevenueWeight the pipeline: what $2M in deals is really worthBeg 3 · ▶ interactive model · ~17 min read Sales & RevenueDiscount leakage: the deal that looks fine at invoice and bleeds at pocketBeg 4 · ▶ interactive model · ~20 min read Sales & RevenueTrade, don't give: concessions, terms, and your walk-away in a live negotiationBeg 4 · ~24 min read Sales & RevenueSet the quota: build the number from capacity, not a wishInt 5 · ▶ interactive model · ~18 min read Sales & RevenueYou get the behaviour you pay for: designing a sales comp plan that doesn't backfireInt 6 · ~25 min read StrategyThe focus trade-off: why a startup wins by saying no to good thingsBeg 4 · ~23 min read StrategyDoes the model make money per order? Marketplace unit economics before scaleInt 5 · ▶ interactive model · ~18 min read StrategyWhere's the moat? Telling a durable advantage from a good quarterInt 5 · ~25 min read StrategyBuild, buy, or partner: entering a market when the cheapest path isn't the fastestInt 6 · ▶ interactive model · ~21 min read StrategyDouble down or cut? Where the next dollar goes across business unitsInt 6 · ▶ interactive model · ~20 min read StrategyPrice war or not? Responding to a competitor's price cutAdv 7 · ▶ interactive model · ~22 min read Supply ChainDays of Cover: the SKU about to stock out isn't the one with the least stockAbsBeg 2 · ▶ runs in browser · ~0.5h Part A Supply ChainStock Turns: the biggest pile of inventory is where your cash goes to sitAbsBeg 2 · ▶ runs in browser · ~0.5h Part A Supply ChainUnits Mismatch: you can't sum a column that mixes cases and eachesAbsBeg 2 · ▶ runs in browser · ~0.5h Part A Supply ChainABC/XYZ Inventory: segment by the money and the variability, not the volumeBeg 3 · ▶ runs in browser · ~1.0h Part A Supply ChainEconomic Order Quantity: how much to order, and when a volume discount is worth the extra stockBeg 4 · ~1.0h Part A Supply ChainThe newsvendor problem: how much to stock when running out and over-ordering cost different amountsBeg 4 · ~0.75h Part A Supply ChainThe Bullwhip Effect: steady demand, wild orders, and finding who amplifiesInt 5 · ~1.0h Part A Supply ChainThe reorder-point trap: why ordering to average demand runs you out of stockInt 5 · ~1.25h Part A Supply ChainDelivery Routing: untangling a route with 2-opt, then splitting a full van into tripsInt 6 · ~1.0h Part A Supply ChainTransshipment: least-cost flow through a network, and modelling a warehouse's throughput limitAdv 7 · ~1.25h Part A Supply Chain & ProcurementReading the reorder point: why the shelf went emptyBeg 3 · ▶ interactive model · ~19 min read Supply Chain & ProcurementThe long tail of spend: consolidate, or leave it alone?Beg 3 · ~25 min read Supply Chain & ProcurementHow much to order at once: the EOQ trade-offBeg 4 · ▶ interactive model · ~18 min read Supply Chain & ProcurementThe cheapest quote isn't the cheapest supplier: total cost of ownershipBeg 4 · ▶ interactive model · ~21 min read Supply Chain & ProcurementHow much safety stock? Service level and the cost of the last few pointsInt 5 · ▶ interactive model · ~20 min read Supply Chain & ProcurementOne supplier or two? Single vs dual sourcing when the part is criticalInt 6 · ~24 min read