Math PicnicFree printable practice
  • Free
  • Grade 8
  • Angles in fives, 25° and up

Angles in a triangle worksheets

Every triangle's three angles come to 180°, and that one fact answers every question on these sheets. Two angles are printed inside the figure and the third is marked x.

Customize Practice Save as PDF New questions

Kid stuck on one? You don’t just get the sheet.

See it worked step by step →Answer it on screen →
  • Answer key included
  • Reopen this exact sheet
  • Letter & A4 ready
Ready to printAngles in a triangle
Angles in a triangle worksheet — Angles in fives, 25° and up, free printable with answer key

The answer key prints on a separate page.

What's on this sheet

The arithmetic is one addition and one subtraction, and that is deliberate. What is being learned is the fact itself, and a child who has to fight the numbers to reach it learns the fight instead. Every angle steps in fives, which keeps the mental arithmetic where the standard wants it.

Why this sheet works

The triangles are drawn to their real angles, which means a protractor would answer them — and that is exactly why the third angle is never printed. A figure here may be honest, but it may not be a lookup. The same rule runs through every angle sheet on this site.

How this one works

One question from this sheet, worked through a step at a time.

The third angle, given 60° and 85°

3 corners=a straight line=180°
60 + 85 =145
60 + 85 =145
180 − 145 =35°
  1. Every triangle's three angles add to 180 — and that is not a number to take on trust. Tear the three corners off any triangle you like and they fit together into a straight line, every time.
  2. Two of them are given: 60 and 85, which is 145 between them.
  3. So the third takes up what is left of the 180: 180 − 145 = 35°.

Pick another skill