Understanding that angles in a quadrilateral add up to 360° and using this to find missing angles.
Where your child meets this in real life: Understanding angles in picture frames, tiles, or building plans
SEAGReady breaks angles in quadrilaterals into 3 steps, taught in order so each skill builds on the last.
Find a missing angle in a quadrilateral when three angles are given
Find missing angles when some angles are right angles or described as equal
Find missing angles using properties of rectangles, parallelograms, and other special quadrilaterals
Three free sample questions from our angles in quadrilaterals course. Every question comes with a full explanation, and hints that guide without giving the answer away.
Aoife is designing a kite for the Belfast school fair. The four corners of the kite have angles of 80 degrees, 95 degrees, 110 degrees, and one unknown angle. What is the missing angle?
Answer: A. 75°
All angles in a quadrilateral sum to 360°. Add known angles: 80 + 95 + 110 = 285° Missing angle: 360 - 285 = 75°
Stuck? Start here: What do all four angles in a quadrilateral add up to?
Declan is tiling a bathroom with quadrilateral tiles. One tile has two right angles and one angle of 80°. What is the fourth angle of the tile?
Answer: A. 100°
Right angles equal 90° each. Add known angles: 90 + 90 + 80 = 260° Missing angle: 360 - 260 = 100°
Stuck? Start here: A right angle equals exactly 90°.
Conor is drawing a parallelogram for his maths homework. One angle measures 70°. What is the angle directly opposite to it?
Answer: A. 70°
In a parallelogram, opposite angles are equal. One angle is 70°, so the opposite angle is also 70°.
Stuck? Start here: In a parallelogram, what is special about opposite angles?
This is the exact interactive worked example your child sees in SEAGReady. Step through it and watch the method build up.
Ciaran is designing a kite for the school fair. The four corners of the kite have angles of 85 degrees, 90 degrees, 105 degrees, and one unknown angle.
What is the missing angle?
85° + 90° + 105° + x° = 360°
Step 1 of 4
Ciaran is designing a kite for the school fair. The four corners of the kite have angles of 85 degrees, 90 degrees, 105 degrees, and one unknown angle.
What is the missing angle?
The missing angle of the kite is 80°.
The key insight: All four angles in ANY quadrilateral always add up to 360 degrees!
Watch out: Using 180° instead of 360°. 180° is for triangles. Quadrilaterals have four angles that sum to 360°.
These are the misconceptions we see most often in angles in quadrilaterals, including the ones our practice questions are specifically designed to catch.
Struggling with angles in quadrilaterals? The real gap is often in one of these earlier topics.
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.