cs-141 — The Rollout Memo

Problem

Your team's script auto-refunds campus print credit under this rule — it is correct and deployed:

refund = 0
if outage_minutes >= 60:      # sustained outage
    refund = 2.00
elif outage_minutes >= 15:    # noticeable blip
    refund = 0.50
# shorter outages: no refund

Outage length comes from a monitoring system that samples every five minutes; a real outage of 14 minutes can be recorded as 10 or 15 depending on where sampling lands. Print Services, who sign off refunds, knows none of this.

Your deliverable — a memo of at most six sentences a non-technical manager can read in one minute — that covers:

1. Who gets what, in plain language.
2. The one sentence about measurement uncertainty that keeps the memo honest (near the boundaries 15 and 60).
3. The one decision the manager must own (the threshold choices).

If the problem is ambiguous anywhere, state the assumption you are making and carry on — a stated assumption is part of a good answer.

Examples

• Input: the deployed rule, the 5-minute sampling fact
• Output: a six-sentence memo covering the rule, the sampling caveat, and the manager's threshold decision

Solve for the worked instance first. Then ask what would change if one number, name, or condition were replaced by something stranger.

What to notice

• The memo's reader must be able to act, so each technical fact earns its sentence by changing a decision or a belief.
• Sampling quantises time: the code's >= 15 quietly means "15 as measured in five-minute quanta" — that is the honesty sentence.
• Thresholds are policy, not physics: the script implements a choice that belongs to the manager, and the memo should hand it back.

Discussion starter

After the solution is revealed, the class spends five minutes on this prompt: "The manager answers: 'just refund anyone with any outage.' Name one consequence that your six-sentence memo had prevented, and where in the memo you would add it."

Constraints and assumptions

• Difficulty: Foundational (plain-language translation of a rule).
• Topics: communication, stakeholders, requirements.
• The script's behaviour is fixed — you are describing it, not changing it.
• Classroom-scale inputs unless the problem says otherwise.
• Time-box: about five minutes for a first attempt; partial answers with clear reasoning are worth more than silent struggling.
• Optional stretch (not required): describe an alternative approach and say when it beats the obvious one.

Hints and extension

• First nudge: underline every number in the script; each one needs a decision about whether it reaches the memo.
• If stuck after three minutes, write the input/output line you expect and trace the smallest example by hand.
• After the reveal, attempt the extension below before the next lecture.
• Extension challenge: rewrite the memo for two audiences at once — the manager and a student newspaper — without losing honesty in either.