3-Digit Addition & Subtraction

Inside the case file

Fall math for September, October and November, including the weeks around Halloween and Thanksgiving. Three digit addition and subtraction with regrouping for 2nd grade and 3rd grade, across five CSI Mini Mystery Detective math case files: two addition cases, two subtraction, and one that mixes both. That covers 3 digit addition with regrouping and subtraction with regrouping as math worksheets and math activities in one no prep download, then spiral review, test prep, math centers, early finishers, homework, morning work and sub plans for the rest of the year. CSI math with full answer keys, and detective activities that need no prep. Each answer clears one suspect from the lineup until a single name is left.

October and November are not easy weeks to hold a class, and this set does that work for you. Each case is a fall story with its own lineup of suspects, and the way through is three digit addition and subtraction with regrouping done carefully, because every answer takes one name off the list. Print the lot on Monday and your morning work is sorted for the week.

The Cases

1. The Fall Leaves - a whole tree stripped in one night
2. The Pumpkin Patch - every last pumpkin has gone
3. The Scarecrows - the scarecrows walk off the field
4. Scattered Leaves - leaves thrown all over the yard
5. The Missing Corn Cobs - the corn maze is stripped bare

What's Inside

• Five case files, each with a crime sheet and its own lineup of suspects
• Two addition cases, two subtraction cases, and one that mixes the two
• Three digit numbers throughout, with regrouping needed on both operations
• 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 one printed page, one crime and one class period. Each suspect in the lineup is tagged with a number, the questions on the left produce those numbers, and a correct answer knocks a suspect out until the last one standing is the culprit. Nothing needs cutting, laminating or charging, which is why these detective activities get used on days when ordinary math worksheets would be handed out. It works as a lesson, in math centers, or left behind for a substitute.

When to Use This Resource

September, October and November is the natural run for this set, and the Halloween and Thanksgiving weeks are where it earns its keep. Regrouping is the skill that fades the moment you stop practicing it, and this keeps it alive without another column of sums. A regrouping slip crosses off the wrong suspect, so students go back and find the column they got wrong instead of handing the page in and hoping.

It covers test prep, homework, math centers, morning work, early finishers, sub plans and homeschool lessons, with a whole class, a small group or one child working alone.

Grade Levels

Written for 2nd grade and 3rd grade, where three digit regrouping sits in the standards. Second graders take the addition cases first, third graders handle subtraction across zeros, and fourth graders use the mixed case as a quick check before moving to four digit numbers.

Why Teachers Love These Cases

• Addition and subtraction sit on separate pages, so you can teach them apart
• Students find their own regrouping slips when the wrong suspect is crossed off
• No prep, and the answer keys make grading quick
• Works with a whole class, a small group, partners, or one student alone

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