3-Digit Addition & Subtraction CSI Mystery Worksheets
Grades 2–5 · The Haunted Hallway
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Inside the case file
October CSI math worksheets with a Halloween case to crack, this CSI Mystery Detective investigation runs on 3 digit addition and subtraction with regrouping from first clue to last. All week things have been going missing from the hallway lockers, and the only useful evidence is a set of numbers. It suits 3rd grade, 4th grade and 5th grade as fun subtraction worksheets or a Halloween math activity, and the routine is print, hand out, done. Students decode sums through a letter key, color the correct arrow, match the locker to its level and add along a path where an odd or even total decides the answer, until the mystery is down to one culprit.
The Case: The Haunted Hallway
All week teachers have been getting the same report: things are going missing from the lockers in the hallway. Students have been blaming each other, loudly, and nobody has got anywhere near the truth. The lockers are on two levels, there are a lot of them, and the only useful evidence is a set of numbers. Work them out and the right locker - and the right culprit - is the one left standing.
What's Inside
- 3 digit subtraction decoded through a letter key
- Subtraction problems used to color the correct arrow to the next clue
- A matching page that identifies which level the locker is on
- 3 digit addition decoded through a letter key
- Addition along a path where an odd or even final total decides the answer
- Full color and black-and-white versions of every page
- Answer keys for the whole case
What Is a CSI Mystery Detective Case?
It plays like a math escape room on paper. Each page asks one question about the locker and the person using it, and hands your students the problems that answer it. They solve, they cross suspects off, and the case closes when one is left - no locks, no props, nothing to reset between classes.
When to Use This Resource
- Halloween week in October, when a normal worksheet will not hold them
- 3 digit addition and subtraction review before or after a unit test
- Math centers, early finishers and independent work
- Emergency sub plans that run themselves
- Back-to-school weeks and end of year review
Grade Levels
Built for 3rd grade, 4th grade and 5th grade. Third graders usually pair up on the four-digit totals; fourth and fifth graders run the case independently. It also suits 6th grade students who need addition and subtraction review without it feeling like going backwards.
Why Teachers Love CSI Mystery Detective Cases
- Zero prep - print and hand out
- Self-checking by design, because a wrong answer breaks the deduction
- A Halloween activity that still does real math
- Works as a whole lesson, a center, or a filler for an awkward afternoon
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