Multiplying Decimals

Inside the case file

Multiplying decimals for 5th grade and 6th grade: five printable CSI Mini Mystery Detective math cases where students multiply on the crime sheet, match the product to a suspect and cross that name off until the culprit is left. These decimal multiplication worksheets are written to 5.NBT.7 and every answer matches exactly one suspect, so a decimal point in the wrong place shows up straight away. No prep, print and go, full answer keys: math activities for the decimals unit, math centers, early finishers, homework and sub plans, any month of the year.

Most classes meet multiplying decimals twice, once in the unit and once in the weeks before testing, and five separate CSI Mini Mystery Detective math cases means you are not handing out the same page both times. The lineup does the checking, so students notice a misplaced decimal point on their own, and the answer keys keep the marking short.

The Cases

1. The Art Gallery - a famous painting is stolen
2. Secret Blueprint Heist - the blueprint is stolen overnight
3. Championship Rugby Ball - stolen the night before the final
4. The Book Shop - a book walks out of the shop
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
• Multiplying decimals on every page, written to 5.NBT.7
• Decimals multiplied by whole numbers and by other decimals, so place value is tested both ways
• 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 hands your class a crime and a lineup, and the only way through it is the math. Work the questions, match each answer to the suspect wearing that number, cross that suspect off, and keep going until one name has not been ruled out. Because the elimination depends on getting the arithmetic right, these detective activities do something a page of math worksheets cannot: students catch their own mistakes. One case fills a class period, with no prep and nothing to assemble.

When to Use This Resource

Bring this out in the middle of the decimals unit, once students can multiply but are still putting the point in the wrong place. That is exactly the error a normal worksheet hides, because the digits look right and the answer is out by a factor of ten. Here a misplaced decimal point crosses off the wrong suspect, so students find the slip themselves and go back to the place value rather than the digits.

It carries 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 alone.

Grade Levels

Written for 5th grade, where 5.NBT.7 sits, 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 decimal division and percentages.

Why Teachers Love These Cases

• Every question is about where the decimal point lands, which is where students go wrong
• Students catch their own errors 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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