Standard Mathematics Primary 5 Angles

Two straight lines AB and CD intersect at point O. Angle AOC = 3x° and angle BOC = (x + 40)°. Find angle AOD.

A 35°
B 65°
C 75°
D 105°
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Worked Solution

Step 1: Angles AOC and BOC lie on straight line AB, so they sum to 180°. 3x + (x + 40) = 180 4x + 40 = 180 Step 2: Solve for x. 4x = 140 x = 35 Step 3: Find angle AOC. AOC = 3(35) = 105° Step 4: Find angle AOD. AOC and AOD lie on straight line CD, so AOC + AOD = 180°. AOD = 180 − 105 = 75° Check (vertically opposite): BOC = (35 + 40)° = 75° = AOD ✓ Answer: 75° Answer: 75°

Correct answer: 75°

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