Finding a Missing Angle in a Quadrilateral: Step-by-Step Example
23 October 2026
Children often find it easier to solve angle questions in quadrilaterals when they know the total of all four angles. This example shows how to use the angle facts rule to work out a missing angle step by step.
Worked example
A quadrilateral has three angles: 75°, 85° and 140°. What is the missing angle?
Step 1: Add the three known angles.
75 + 85 = 160
160 + 140 = 300
Step 2: Subtract this sum from 360° to find the missing angle.
360 - 300 = 60
Key insight: The four angles in a quadrilateral always add up to 360°.
The correct answer is 60°.
Now your child can spot when to add or subtract angles in a quadrilateral, using the 360° rule. They are ready to try similar questions and build confidence with angles in quadrilaterals.
