Adding and Subtracting Decimals

Inside the case file

Adding and subtracting decimals worksheets for 5th grade, used again in 6th: five CSI Mini Mystery Detective math cases where students line up the decimal points, find the suspect with that answer and cross the name off until one is left. Every answer matches a single suspect, so a misplaced decimal point shows up on the lineup before it shows up on a test. Print and go with full answer keys: math activities for the decimals unit, then math centers, early finishers, homework, morning work, test prep and sub plans all year.

Five CSI Mini Mystery Detective math cases in one file is a week of decimal practice without handing out the same page twice, and the lineup does the checking so you are not marking the same slip twenty times. Use one with the whole class after the lesson, then keep the rest for early finishers and the sub folder.

The Cases

1. The Museum Theft - the museum loses its treasure
2. Secret Blueprint Heist - the blueprint is stolen overnight
3. Missing Secret Sauce - the kitchen loses its famous recipe
4. Championship Soccer Ball - gone hours before the big game
5. Experimental Lab - somebody sabotaged the whole lab

What's Inside

• Five case files, each with a crime sheet and its own lineup of suspects
• Adding and subtracting decimals on every page, to 5th grade standard
• Numbers with different numbers of decimal places, so students have to line them up
• Each answer matches one suspect and no other, so the page checks itself
• A full answer key for every case
• Print and go: no cutting, no laminating, nothing to prepare

What Is a CSI Mini Mystery Detective?

A CSI Mini Mystery Detective is a printable case with a lineup of suspects, each carrying a number. The questions on the crime sheet produce those numbers, a correct answer strikes one suspect off, and the last name standing is the culprit. Because the elimination depends on the arithmetic, these detective activities catch mistakes that a page of math worksheets would let through. One case takes a class period, with nothing to prepare and nothing to buy.

When to Use This Resource

Use this in the decimal unit once the class can add and subtract but is still lining the columns up by the last digit instead of the point. That single habit is behind most of the wrong answers, and it hides beautifully on a normal worksheet. Here it crosses off the wrong suspect, so the student sees the problem and goes back to the place value rather than the arithmetic.

It suits test prep, homework, math centers, morning work, early finishers, sub plans, homeschool lessons and spiral review, with a class, a small group or one student.

Grade Levels

Written for 5th grade, where adding and subtracting decimals sits in the standards, and used with 6th graders as fluency practice. Fourth graders take it once decimal place value is secure, and 7th graders use it as a refresher before operations with negatives.

Why Teachers Love These Cases

• Mixed decimal places, so students have to line the points up themselves
• Students catch their own errors when the wrong suspect comes off the lineup
• No prep, and the answer keys make grading quick
• Works with a whole class, a small group, partners, or one student alone

Love this resource?

Follow Kiwiland Education to discover more CSI Mini Mystery Detective cases, no-prep math activities, and detective-themed printables for elementary and middle school classrooms.

Follow Kiwiland Education on TPT ↗

Buy · $4