Math Detective
Someone's number doesn't add up. Check each person's receipt, tip or count with one calculation, then name the mistake.
Case of the day
Today's inspector case
Four people, one mistake, the same case for everyone today.
New case
No cases solved at this rank yet.
How to play
- Read the case file: each person says what they paid, tipped or counted.
- Each clue is one calculation that checks one person's number. Use the calculator beside it, or work it out yourself.
- Your answer goes in the notebook next to their claim. Two tries per clue, then the answer and the working are shown.
- When every claim is checked, pick the person whose number doesn't match. You get one guess.
Scoring
100 points for a clue right first time, 50 on the second try, and 200 for naming the right person. Hints are free: the point is to learn how the calculation works.
The mistakes are real ones
Every wrong number comes from an everyday slip: taking 25 dollars off instead of 25%, working out 10% and calling it a 20% tip, adding the tax rate as dollars, or forgetting the tax altogether. The end of each case explains what went wrong, so you can spot it on a real receipt.
Ranks
Rookie cases have three people and one-step clues. Inspector cases have four people and add two-step clues: a discount, then tax on the sale price. The case of the day is an inspector case.
Your scores
Cases solved and best scores are saved in this browser only. No account, and nothing is sent anywhere.