Addition & Subtraction CSI Mystery Worksheets | Grades 2–5 | The Valentine's Surprise Card

Valentines Day CSI math worksheets for February, built around addition and subtraction with two-digit, three-digit and four-digit numbers and wrapped in a CSI Mystery Detective case. Someone left an unsigned envelope in a desk before the bell, and 2nd grade and 3rd grade students find out who by getting the math right. It is a fun subtraction and addition activity that doubles as solid practice, and the mystery keeps them working long after a plain page would have lost them. Zero setup - print and hand it over. Correct answers get colored, a cryptogram gets cracked, and a chain of linked clues narrows the line-up one suspect at a time. Answer keys included.

The Case: The Surprise Card

Valentines Day is finally here and you have worn your best clothes to school for it. The bell goes, you open your desk for your math book, and there is an envelope sitting on top of it that you did not put there. No name on it. Somebody in this room got up early, and your students are going to work out which one.

What's Inside

• Deciding which number problems are correct and coloring the right answers
• A cryptogram that reveals the color of a strand of hair left in the envelope
• Multi-step problems where the last answers give a shoe size
• Checking worked answers for errors and tallying which are correct
• A sequence of linked clues that builds to one final number
• 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 is a printable math activity dressed as police work. Your class gets a crime, a line-up of suspects and a page of math worksheets, and the answers do the eliminating until one name is left. It is a math escape room without the locks, the app or the prep. Unlike a practice page it will not let a wrong answer pass quietly - the case stops closing - so students check as they go. Use it for a lesson, in math centers, or as detective activities for early finishers.

When to Use This Resource

• Valentines Day in February, when a normal worksheet will not hold them
• Addition and subtraction review before or after a unit test
• Math centers, early finishers and independent work
• Emergency sub plans that run themselves
• End of year review, when attention is thin and the work still has to happen

Grade Levels

Built for 2nd grade and 3rd grade. Second graders usually pair up on the larger numbers; third graders run the case independently. It also suits 4th grade students who need addition and subtraction review in a form that does not look like going back a year.

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 Valentines activity that still does real math
• Works as a whole lesson, a center, or a filler for an awkward afternoon

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