4024/12 Oct/Nov 2025, Question 3: Angles in a Quadrilateral
Cambridge O Level Mathematics 4024 · Paper 12 (Non-calculator) · Non-calculator · 4 marks
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The question, in short
In parallelogram ABCD, E lies on AB with EC equal to BC. Given angle ECB is 40° and angle DEC is 60°, work out the size of angle ADE, labelled x.
Summarised in our own words. Use the official paper for the exact wording and the diagram.
Solution · 4 marks
- 1EC = BC, so angle CEB = angle CBE = (180 − 40) ÷ 2 = 70°
- 2Angle AED = 180 − 60 − 70 = 50° (angles on a straight line)
- 3Angle DAE = 180 − 70 = 110° (co-interior angles, AD parallel to BC)
- 4x = 180 − 110 − 50 = 20
Answer20
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