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Compare buying and renting your textbooks

  • For College students
  • You practice Showing an example of what you want
  • Time about 5 minutes

About this exercise

You need three textbooks this semester. Compare buying used (then selling back at the end) with renting. Get exactly 3 numbered lines in plain text, under 70 words: 1. the buy-used cost after sell-back, with the math; 2. the rental cost, with the math, using the corrected rental price; 3. which costs less and by how much. No advice. Write a prompt that gets you exactly that.

Common mistakes when you ask AI for this

  • Missing the correction. The AI uses $40 for the PSY 101 rental. Try: Add: "PSY 101 rental is now $50."
  • Forgetting the sell-back. The AI compares the used price to the rental and ignores the money you get back. Try: Say: "Buy used minus the buyback estimates."
  • No math shown. The AI gives totals with no working, so you can't check them. Try: Show it: "1. Buy used: $120 + $80 + $40 = $240 - $90 buyback = $150".
  • Getting advice. The AI weighs pros and cons and nudges you toward one option. Try: Add: "The last line only says which costs less and by how much. No advice."
  • Trusting the AI to count words. AI is bad at counting. Ask for "under 70 words" and it often lands well over. Try: Cap each part: "each line under 18 words."

What a strong prompt includes

  • Uses the correction
  • Counts the sell-back
  • Shows the math
  • Sets the number of lines
  • Sets a word limit

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