Foundation Mathematics Primary 6 Angles

A school flag at the morning assembly is shaped like a triangular pennant ABC. The angle at vertex A is 75° and the angle at vertex B is 50°. Find the size of the angle at vertex C.

A 55°
B 105°
C 125°
D 130°
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Worked Solution

Step 1: Recall the rule. The three interior angles of any triangle add up to 180°. ∠A + ∠B + ∠C = 180°. Step 2: Add the two given angles. ∠A + ∠B = 75° + 50° = 125°. Step 3: Subtract from 180° to find ∠C. ∠C = 180° − 125° = 55°. Check (reverse): 55° + 75° + 50° = 180° ✓ Final answer: ∠C = 55°. Answer: 55°

Correct answer: 55°

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