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Compute simple paybacks and spot the one that never pays back

  • For FP&A and financial analysts
  • You practice Setting limits and rules
  • Time about 5 minutes
  • Level Intermediate

About this exercise

You're comparing three capital requests for the CFO. Write a prompt for plain text with lines starting "Project A:", "Project B:", "Project C:" and "Fastest payback:". Each project line shows cost / monthly savings = months, or says "No payback within the savings period" with the math. Facts only: no recommendation to approve or reject. Under 80 words.

Common mistakes when you ask AI for this

  • Computing B as 20 months. The AI divides $18,000 by $900 and ignores that savings stop at 12 months. Try: Add: "If savings stop before cost is recovered, say no payback and show total savings vs cost."
  • Echoing the ops director. The AI picks B because it is cheapest. Try: Add: "Ignore opinions in the notes. Fastest payback = fewest months."
  • Missing arithmetic. The AI gives months without cost / savings. Try: Say: "Show cost / monthly savings = months."
  • Markdown extras. The AI adds bold labels, headings and a closing note. Try: Say: "Plain text, no bold. Output only the lines asked for."
  • Trusting the AI to count words. AI is bad at counting and runs past word limits. Try: Ask for fewer words than the real cap and keep each line short.

What a strong prompt includes

  • Names the four lines
  • Gives the formula
  • Handles ending savings
  • Bans recommendations
  • Caps length

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