Addition Within 100 CSI Mystery Worksheets
Grades 2–6 · Back to School
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Inside the case file
September CSI math worksheets for 2nd grade and 3rd grade on multiples of 3 and 5, even numbers and a hundreds chart, run as a CSI Mystery Detective case called The Suspect Number. It holds up just as well as 4th grade math review. Everything prints ready to use in color or black and white, with answer keys for every page. The only fact at the start is that the mystery number is under 100, so students run a real investigation - evidence, forensics, line-up, interrogation - shading multiples, sorting out the even numbers and cross-matching witness numbers until two suspects are left and one final puzzle decides it.
The Case: The Suspect Number
The only thing known at the start is that the number is under 100. That leaves rather a lot of them. Your students work it the way an investigation actually runs: evidence, then forensics, then a line-up, then interrogation, with the suspect list getting shorter at every stage until two numbers are left arguing about which of them did it.
What's Inside
- A letter-and-number cipher that decodes the opening message
- Shading the multiples of 3 and 5 on a hundreds chart
- Working out which of the remaining suspects are even numbers
- Cross-matching the witness numbers against the evidence so far
- A final puzzle that separates the last two suspects
- Full color and black-and-white versions of every page
- Answer keys for the whole case
What Is a CSI Mystery Detective Case?
A CSI Mystery Detective case turns a page of math into evidence. Students solve, and each correct answer removes one candidate until a single one is left. There is nothing to unlock, download or prepare - it is a math escape room made of paper. Detective activities also police themselves, which ordinary math worksheets never do: an error leaves two possibilities alive, so the class rechecks. A math activity that carries a lesson, a center rotation, or a sub plan.
When to Use This Resource
- Introducing or consolidating multiples and even numbers
- Hundreds chart work that is not coloring for its own sake
- 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 2nd grade, 3rd grade and 4th grade. Second graders usually want the hundreds chart explained once before starting; third and fourth graders run the whole investigation independently. It also gives 5th grade students who are shaky on multiples a way to rebuild without going back to a plain worksheet.
Why Teachers Love CSI Mystery Detective Cases
- Zero prep - print and hand out
- Self-checking by design, because an early error shows up later
- Number work students will actually finish
- Works as a whole lesson, a center, or a filler for an awkward afternoon
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