SEAGReady
Shape and SpaceP7 level22 questions in the full course

Angles in TrianglesSEAG Practice Questions

Understanding that angles in a triangle always add up to 180° and using this to find missing angles.

Where your child meets this in real life: Calculating angles in roof trusses, triangular structures, or navigation

What your child needs to know

SEAGReady breaks angles in triangles into 3 steps, taught in order so each skill builds on the last.

  1. 1

    Two Angles Given

    Find the missing third angle when two angles of a triangle are given

  2. 2

    Isosceles and Equilateral

    Find angles in isosceles and equilateral triangles using equal-angle properties

  3. 3

    Reasoning with Internal Angles

    Solve multi-step problems using only internal triangle-angle properties

Try these SEAG-style questions

Three free sample questions from our angles in triangles course. Every question comes with a full explanation, and hints that guide without giving the answer away.

Question 1Confidence builder

The triangle shown has angles of 60° and 65°. What is the third angle?

A triangle with two interior angles labelled 60 degrees and 65 degrees and the third angle marked with a question mark.
Answer choices for question 1
Question 2Confidence builder

The isosceles triangle shown has an apex angle of 50°. What is the size of each base angle?

An isosceles triangle with equal-side marks, an apex angle of 50 degrees, and both equal base angles labelled x.
Answer choices for question 2
Question 3Confidence builder

In triangle PQR, angle P is 45 degrees and angle Q is 70 degrees. What is angle R?

Triangle PQR has angle P labelled 45 degrees, angle Q labelled 70 degrees, and interior angle R marked with a question mark.
Answer choices for question 3

Try the lesson: Two Angles Given

This is the exact interactive worked example your child sees in SEAGReady. Step through it and watch the method build up.

Jack is designing a triangular flag for his school's sports day. Two of the angles measure 55 degrees and 70 degrees.

What is the third angle of the flag?

55° + 70° + ? = 180°

Add the known angles
1

The two given angles are 55° and 70°

Step 1 of 4

Prefer to read? See every step written out

Jack is designing a triangular flag for his school's sports day. Two of the angles measure 55 degrees and 70 degrees.

What is the third angle of the flag?

  1. 1

    Add the known angles

    • The two given angles are 55° and 70°
    • Add them together55° + 70° = 125°
  2. 2

    Subtract from 180 degrees

    • Angles in a triangle always add to 180°
    • Find the missing angle180° − 125° = 55°

The third angle of the flag is 55°.

The key insight: Every triangle's angles add to exactly 180 degrees - no matter what shape it is!

Common mix-up: Using 360° instead of 180°. 360° is for angles around a point. Triangles always use 180°.

Mistakes to watch for

These are the misconceptions we see most often in angles in triangles, including the ones our practice questions are specifically designed to catch.

  • Thinking different triangle types have different angle sums
  • Forgetting to add all three angles before subtracting from 180
  • Confusing with angles on a straight line rule

Build these skills first

Struggling with angles in triangles? The real gap is often in one of these earlier topics.

Angles on a Straight LineClassify Triangles

More shape and space practice

Name 2D ShapesLine Types and PropertiesDescribe Shape PropertiesClassify QuadrilateralsUnderstand PolygonsLines of Symmetry
22 questions on this topic alone

Master angles in triangles and everything it unlocks

SEAGReady finds the exact step where your child gets stuck, teaches it with worked examples like the one above, and brings it back for review so it sticks.

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