{"id":"life-col-textbook-buy-vs-rent","audience":"college","category":"everyday-life","track":"life","technique":"examples","title":"Compare buying and renting your textbooks","free":false,"task":"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.","materialLabel":"Bookstore prices (attached to your prompt automatically)","material":"CAMPUS BOOKSTORE - SPRING 2027 (fictional)\n\nBIO 120 - Biology: Life on Earth\n  Used: $120 | Rental: $60 | Buyback estimate: $50\n\nPSY 101 - Intro to Psychology\n  Used: $80 | Rental: $40 | Buyback estimate: $30\n\nENG 102 - Writing and Argument\n  Used: $40 | Rental: $25 | Buyback estimate: $10\n\nBOOKSTORE NOTE (posted Nov 5): \"Correction: the PSY 101 rental price is $50, not $40.\"\n\nMY NOTES\n- I'll sell back all three if I buy them.\n- Roommate says digital access codes are cheaper, but my classes say print is fine.\n- Rentals must be returned by May 15.","rules":[{"type":"numberedItems","count":3},{"type":"maxWords","max":70},{"type":"plainText"}],"mistakes":[{"title":"Missing the correction","why":"The AI uses $40 for the PSY 101 rental.","fix":"Add: \"PSY 101 rental is now $50.\"","checks":["r1"]},{"title":"Forgetting the sell-back","why":"The AI compares the used price to the rental and ignores the money you get back.","fix":"Say: \"Buy used minus the buyback estimates.\"","checks":["r0"]},{"title":"No math shown","why":"The AI gives totals with no working, so you can't check them.","fix":"Show it: \"1. Buy used: $120 + $80 + $40 = $240 - $90 buyback = $150\".","checks":["r0","numberedItems"]},{"title":"Getting advice","why":"The AI weighs pros and cons and nudges you toward one option.","fix":"Add: \"The last line only says which costs less and by how much. No advice.\"","checks":["r2","plainText"]},{"title":"Trusting the AI to count words","why":"AI is bad at counting. Ask for \"under 70 words\" and it often lands well over.","fix":"Cap each part: \"each line under 18 words.\"","checks":["maxWords"]}],"promptHints":[{"label":"Uses the correction","patterns":["\\$?50","correct","psy"]},{"label":"Counts the sell-back","patterns":["buyback","sell.?back","minus"]},{"label":"Shows the math","patterns":["\\+","show.{0,15}(math|work)","add"]},{"label":"Sets the number of lines","patterns":["\\b(3|three)\\b.{0,20}(lines?|numbered|items?|steps?)"]},{"label":"Sets a word limit","patterns":["\\d+\\s*words","word (limit|count)"]}],"hint":"Buying looks pricier until you count what you get back. Tell the AI every piece to count, which price is current, and show it one line.","rubricLabels":["Line 1 gives buying used as $150 after sell-back ($240 - $90)","Line 2 gives renting as $135 using the corrected $50 PSY 101 rental ($60 + $50 + $25), not $125","Line 3 says renting costs $15 less, and the answer gives no advice beyond the numbers"]}