Measuring Angles with a Protractor

Inside the case file

These measuring angles with a protractor worksheets for 4th grade are ten CSI Mini Mystery Detective math cases with a lighthouse theme. They cover reading angles in degrees, angle addition, and complementary and supplementary angles. Use these geometry activities in math centers, morning work, small groups and homework. They're no prep, and there's an answer key for every case.

Every case is set around a lighthouse on a stormy coast. Students read angles on both protractor scales, find the angle between two rays, and work out missing angles on a straight line or inside a right angle. They match each angle to a suspect and cross that name off, which means they check their own measuring as they go. Every page is self-checking.

What's Inside

• Ten one-page detective cases on measuring angles, each with an answer key
• A large, clear protractor on every page, marked to the nearest degree
• Cases that build from reading both scales to angles between two rays, adding angles, straight lines, right angles and obtuse angles
• A reference page on using a protractor, choosing the right scale, and adding and subtracting angles
• A contents page, teacher instructions, a detective case log and a certificate of achievement
• 30 black and white pages, ready to print

The Cases

1. The Dark Lighthouse - reading angles on both scales
2. The Stolen Lens - reading angles to the nearest degree
3. The Cut Anchor Chain - the angle between two rays
4. The Missing Key - two rays, to the nearest degree
5. The Foghorn Prank - adding angles together
6. The Fake Sea Map - missing angles on a straight line
7. The Runaway Rowboat - missing angles in a right angle
8. The Fake SOS - every kind of angle, to the degree
9. The Shipwreck Gold - obtuse angles
10. The Ghost Ship - mixed angle problems

When to Use This Resource

The cases build from reading a protractor to mixed angle problems. You can hand out one case at a time through the geometry unit or pull a single page when a group needs more protractor practice. The first cases suit students holding a protractor for the first time, and the later ones stretch a class that is ready for unknown angles and angle addition. Guided math groups, test prep, sub plans, early finishers and homeschool lessons all work too.

Grade Levels

Written for 4th grade, where students first measure angles in whole-number degrees and learn that angles add together. It also makes a quick review for 5th graders before they classify and measure angles in more detail.

Why Teachers Love Mystery Detectives

• Zero prep
• Every correct angle crosses off a suspect
• Leveled cases
• A lighthouse mystery with a ghost ship
• Black and white pages, easy to copy

Want more cases like these?

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