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33. Multi-source reasoning

Skim all tabs first for what lives where; answer questions by targeted lookup, not memory.

EmailTableChartMap of what lives where:Email: the rules and exceptionsTable: the shipment costsChart: monthly totalstargeted lookupSkim all tabs once, then jump straight to the source.Know where each fact lives before answering.

Core ideas

- Skim ALL tabs first, but only to learn what lives where (a map, not the content). Then answer each question by targeted lookup.
- Never answer from memory of a tab; flip back and confirm the exact number or condition.
- Most MSR questions require combining exactly two sources; identify which two before computing.

Worked example 1

Tab 1 (Email from operations): "The Harlow warehouse can ship at most 400 crates per week. Rush orders must ship within 2 days." Tab 2 (Rate table): standard shipping $8 per crate; rush shipping $14 per crate. Tab 3 (Order log): Week 1 orders were 250 standard crates and 100 rush crates.
Question: What was the total shipping revenue in Week 1, and was the warehouse within capacity?

Show solution

The map from skimming: capacity lives in Tab 1, prices in Tab 2, quantities in Tab 3. Targeted lookup: revenue = 250 x 8 + 100 x 14 = 2000 + 1400 = 3400 dollars. Capacity check combines Tab 3 with Tab 1: 250 + 100 = 350 crates, which is at most 400, so yes, within capacity. Two tabs per question, confirmed by flipping back, not from memory.

Worked example 2

Tab 1 (Policy memo): "A course runs only if at least 12 students enroll. Lab courses also require a certified instructor." Tab 2 (Enrollment list): Pottery 15 students, Robotics Lab 14 students, Watercolor 9 students. Tab 3 (Staff roster): certified lab instructors available: 1 (assigned to Chemistry Lab, 13 students).
Question: For each course in Tab 2, will it run? Yes or No.

Show solution

The rule lives in Tab 1: 12+ students, plus a certified instructor if it is a lab. Pottery: 15 students, not a lab, so Yes. Robotics Lab: 14 students clears enrollment, but Tab 3 shows the only certified lab instructor is assigned to Chemistry Lab, so no instructor is available, so No. Watercolor: 9 students is below 12, so No. Each verdict came from re-checking the specific tab, and the lab condition needed two tabs combined.

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