3-Digit Addition & Subtraction with Regrouping

Inside the case file

Your 2nd and 3rd grade students can practice 3 digit addition and subtraction with regrouping in these ten CSI Mini Mystery Detective math cases with a spy theme. Each page has addition with regrouping and three digit subtraction with regrouping on it, including subtraction across zeros. Use them in math centers, for morning work, as homework or as early finisher work. They're no prep, and each case comes with its own answer key.

A page holds 16 problems, eight additions and eight subtractions, and every problem needs regrouping. Some regroup only the ones, some only the tens, and some both. Two subtractions a page cross a zero, like 700 minus 584. Students match each answer to a suspect's ID badge and cross that suspect off. The work is self-checking: the usual slips, such as forgetting to carry or not taking the ten away after a trade, don't match a badge. With every answer right, one suspect is left, and that's the villain.

What's Inside

• 10 one-page spy cases with 16 problems on each, 160 problems in all
• An answer key for every case
• Sums of 999 or less. Every subtraction answer is a three digit number
• Regrouping in the ones, in the tens, in both, and across zeros
• A How to Regroup page set out in hundreds, tens and ones, with 368 + 475 and 532 - 278 worked step by step
• Teacher instructions, a contents page and a Detective's Case Log
• A Master Spy certificate
• 30 pages, made to print in black and white

The Cases

1. The Missing Spy Drone - a drone gone from the rooftop launch pad
2. The Stolen Memory Card - secret plans missing from the gadget lab
3. The Gummed-Up Camera - chewing gum over the hallway security camera
4. The Open Vault Door - the Spy Bank vault found open at midnight
5. The Missing Flash Drive - the agents' secret names taken from the code room
6. The Muddy Footprints - a trail from the garden into the map room
7. The Erased Recording - a secret meeting wiped before anyone heard it
8. The Empty Evidence Bag - an evidence bag left empty on the lab table
9. The Cracked PIN Pad - someone tapped in the PIN and took the spy car
10. The Raided File Drawer - the records room drawer left in a mess

When to Use This Resource

Bring these out once your class can regroup with three digit numbers, since addition and subtraction share each page. The How to Regroup page can go up on the board, or into a folder for students who want the steps beside them. A single case suits a small group, a test prep review or a sub day. Teachers in 4th grade can use the pack for review and intervention before multi-digit work, and it also works for homeschool practice.

Grade Levels

Made for 2nd grade (2.NBT.B.7) and 3rd grade (3.NBT.A.2), the two grades where adding and subtracting within 1,000 is taught. In 4th grade it makes a regrouping review.

Why Teachers Love Mystery Detectives

Each Mystery Detective pack runs the same way, so a class that has finished one case can start the next without new instructions, even from a different pack. No case depends on another one. You can choose the one that suits the lesson. The villain at the end gives students something to aim for, and checking a page against the key takes a minute.

Want more cases like these?

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

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