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10 printable sets · answer key on every set

Finding Unknown Angles Worksheets

  • CCSS 4.MD.C.7
  • 12 problems per set
  • Answer key included

What this skill is

Finding a missing angle when a big angle is split into parts: the parts add up to the whole angle.

When it comes up: Fourth grade, alongside measuring with a protractor.

The mistake to watch for

Adding the two known numbers instead of subtracting one part from the whole angle.

How to help

Draw the big angle and mark the split. Write the whole, the part you know, and a box for the part you do not know.

Next: Drawing and measuring angles with a protractor.

A worked example

A 90° angle is split into two parts, and one part is 35°. The parts must add up to 90°, so the other part is 90° − 35° = 55°.

Words to know

angle
The space between two lines that meet at a point, measured in degrees.
degree
The unit for measuring angles. A square corner is 90 degrees (90°).
protractor
A tool shaped like a half circle that is used to measure and draw angles.
subtract
To take one number away from another to find how many are left.
whole
All of something. In 3 + 4 = 7, the whole is 7.

Practice

Find the missing angle.

Showing Set 1 · 12 problems

  1. An angle of 150° is split into two parts. One part is 130°. How many degrees is the other part?
  2. An angle of 135° is split into two parts. One part is 55°. How many degrees is the other part?
  3. An angle of 60° is split into two parts. One part is 40°. How many degrees is the other part?
  4. An angle of 90° is split into two parts. One part is 20°. How many degrees is the other part?
  5. An angle of 150° is split into two parts. One part is 110°. How many degrees is the other part?
  6. An angle of 60° is split into two parts. One part is 50°. How many degrees is the other part?
  7. An angle of 60° is split into two parts. One part is 5°. How many degrees is the other part?
  8. An angle of 180° is split into two parts. One part is 140°. How many degrees is the other part?
  9. An angle of 135° is split into two parts. One part is 20°. How many degrees is the other part?
  10. An angle of 90° is split into two parts. One part is 30°. How many degrees is the other part?
  11. An angle of 90° is split into two parts. One part is 35°. How many degrees is the other part?
  12. An angle of 100° is split into two parts. One part is 50°. How many degrees is the other part?

Download this set12 problems · answer key included PDF

Answer key
  1. 20°
  2. 80°
  3. 20°
  4. 70°
  5. 40°
  6. 10°
  7. 55°
  8. 40°
  9. 115°
  10. 60°
  11. 55°
  12. 50°

All 10 sets

Each set is a different list of 12 problems with its own answer key. Use the buttons above to look at one on this page, or download any of them as a PDF.

How these sheets were made
  • Problems are generated for each set and checked against 4.MD.C.7 before the sheet is built — no duplicates, and every problem falls inside the standard's number range.

Common Core State Standards © 2010 National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.