Week 16: Synthesis Presentations & Course Close

This week’s big question: every problem so far arrived with a chapter attached. Real ones don’t. When a messy situation lands on your desk with no label, how do you pick the method, check that it worked, and hand back a recommendation somebody can act on?

This is the last week of class, and it carries no new content: no new chapter, no graded take-home, no submitted group practice, and no in-class checkpoint. Both sessions are given over to the course-synthesis presentations. Ten minutes each is long enough to actually show the work, which means about five presenters per session, drawn at random in the room. Come ready both days: each session is worth 1 point for being there and taking part, drawn or not.

There is no finals-week meeting. Our last class is Wed Dec 9. The 14-point synthesis submission is due Sun Dec 13, after you present, and nothing is scheduled during the Dec 14–18 final-examination period.

Before the week

• Read: no new chapter. Skim your notes, solved workbooks, and the Key Concepts from Weeks 1–15.
• Be ready to present on both days. Ten minutes, five beats, the live workbook plus a slide or two.
• Work through the recap reference below on your own. It used to be a Monday lecture; the sessions are now presentations, so it is yours to read at your own pace.
• Cumulative warm-up: use this ungraded check to identify the topics that need another look.

Recap reference: choose, solve, and check

Self-study. Monday opens with a ten-minute warm-up drawn from the puzzle below, but the rest is here for you to work through whenever you like. None of it is new material.

🧩 Puzzle

The director’s desk. A director drops by: “Our delivery program costs too much, demand swings every month, and some sites keep running short. What should we do?” No table, no numbers, no chapter number. Which question do you sharpen first, which method answers it, and what evidence would make your recommendation credible?

Notice what is not hard here. Operating Solver is not hard. Evaluating \((o + 4m + p)/6\) is not hard. The hard part is that the director asked three questions at once and labelled none of them. Turning a complaint into an answerable question, and then matching that question to a tool you already own, is its own skill, and it is the one this week drills.

Build the skill 1: run the five-step cycle you have used all term

Every topic in this course has been the same cycle wearing different clothes:

1. Observe the system. Name the symptom, the decision-maker, and who else is affected.
2. Define the problem. Turn “costs are too high” into something you could actually answer, “Which shipping plan meets every site’s demand at minimum weekly cost?”
3. Construct the model. Name the choices, the objective, the limits, and where the input data comes from.
4. Solve and check it. Compute it, verify it, and move at least one plausible input to see what happens.
5. Recommend and implement. Say what to do, then say what would change your mind.

Steps 2 and 5 are the ones students skip, and they are exactly the two that keep correct arithmetic from answering the wrong question.

Build the skill 2: listen for the structure, not the vocabulary

A signal gives you a candidate, not an answer. Before you commit, check that the data and the assumptions actually fit. Starting with whether the quantities you need are known (deterministic) or uncertain (probabilistic), because that single question separates Week 7’s LP from Week 4’s payoff table.

Build the skill 3: fold back a decision one more time

A public-health office must choose one preparedness plan before it knows whether demand will be severe (\(0.40\)) or mild (\(0.60\)). Payoffs are in thousands of dollars of net public value. Fold back each alternative:

• Stockpile big: \(0.40(120) + 0.60(-30) = 30\)
• Stockpile small: \(0.40(70) + 0.60(40) = 52\)
• Wait and see: \(0.40(-50) + 0.60(90) = 34\)

The small stockpile wins on expected value at \(52\). But finishing there is the mistake: where did the \(0.40\) come from, and does a dollar of “net public value” really capture who goes unserved in a severe season? The arithmetic took ten seconds. Those two questions are the job.

Build the skill 4: back to where the term started

A student organization pays \$1,800 to reserve a venue, spends \$7 per attendee, and charges \$25 per ticket. The contribution margin is \(25 - 7 = 18\) dollars per attendee, so

One hundred attendees. The same one-line skill from Week 1, and the same caveat: it is a threshold to compare against expected turnout, not a promise anyone will show. If the venue seats 80, the model just told you the event cannot break even at that price. Move the sliders and watch the threshold shift.

In practice: your method choice is a claim you have to defend

• Start with the decision, not the software. “I used Excel” names no method and explains nothing. “I used a transportation model because every site’s demand had to be met from a fixed set of depots” does both.
• Separate predicting from choosing. A forecast estimates what will happen; an optimization or decision model recommends what to do about it. Confusing the two is how you end up optimizing a guess.
• Find the assumption the answer rests on. Probabilities, linear relationships, stable trends, task durations, all estimates. Move the one that matters most and see whether your recommendation survives.
• Two models beat one when the question has two halves. Forecast the demand first, then route supplies for it. That is not overkill; that is the director’s question answered properly.

Back to the puzzle

The director asked three questions in one breath, and each points somewhere different: “what will demand be?” is forecasting, “how should we route deliveries?” is transportation, and “does this still hold if fuel goes up?” is a sensitivity check. So pick one decision, name the method whose structure matches it, solve it, and report two things: the action, and the conditions under which the action stops being right.

Session 1: Mon, Dec 7 · The draw, and the first presentations (TBD)

A short warm-up on the director’s-desk puzzle above, then we draw five names and those five present, ten minutes each with a question or two after.

Everyone in the room earns the session’s point, drawn or not, so the session is worth your attention either way: these are your classmates’ real models, and the questions asked here are the ones your own submission has to survive. See Course Synthesis for the format and the rules of the draw.

Session 2: Wed, Dec 9 · The rest of the presentations, and the course close (TBD)

A second draw and five more presentations, then we close the course: a short cumulative look back across the methods, the course evaluation, and anything still unresolved. Your synthesis submission is due the following Sunday, so bring questions about it while we are all still in the room.

Cumulative self-check

One last ungraded check across the term’s methods and interpretations. Retry it freely, and treat anything you miss as your revision list before you finish the synthesis.