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Show cohort retention math step by step

  • For Business analysts
  • You practice Catching mistakes and made-up facts
  • Time about 5 minutes
  • Level Advanced

About this exercise

Your growth lead wants the signup cohort retention table checked, plus the blended month-1 number and the blended month-2 number for the cohorts that have it. Retention is retained users divided by cohort size, rounded to a whole percent; the blended numbers are weighted by cohort size (total retained over total users) with one decimal. Write one plain-text line per available cohort month like 'Jan M1: 260 / 400 = 65%', then two final lines labeled Weighted M1: and Weighted M2: showing the sums. Under 130 words, no commentary, and skip months that are not available yet.

Common mistakes when you ask AI for this

  • Averaging the percentages. The AI averages 65, 66 and 50 and gets 60.3% instead of weighting by size. Try: Add: "Weighted by cohort size: total retained divided by total users."
  • Hiding the arithmetic. The AI jumps to percentages and some come out wrong. Try: Add: "Write each line like Jan M1: 260 / 400 = 65%."
  • Padding with unavailable months. The AI fills Feb M3 and Mar M2 with guesses and adds insights. Try: Add: "Skip months marked not available. No commentary."
  • Leaving the format to chance. The AI picks its own length and layout unless told the exact shape. Try: Add: "Plain text, no bold or headings."
  • Trusting the AI to count words. AI is bad at counting. Ask for a total word limit and it often lands over it. Try: Cap each part instead, for example "each line under 15 words."

What a strong prompt includes

  • Shows the line shape
  • Asks for a weighted blend
  • Uses the cleaned Jan size
  • Skips missing months
  • Rules out commentary

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