Standard Mathematics Primary 5 Angles

At a Tampines bus stop, three signpost arms extend outward from a single point on the top edge of the signboard, forming three angles along the straight top edge. Two of the angles are 48° and 67°. What is the size of the third angle, marked ∠a, in degrees?

A 23°
B 65°
C 115°
D 132°
Show Worked Solution

Worked Solution

Step 1: Recall the rule — angles on a straight line add up to 180°. Step 2: Write the equation for the three angles meeting on the top edge of the signboard: ∠a + 48° + 67° = 180°. Step 3: Add the two known angles: 48° + 67° = 115°. Step 4: Subtract from 180°: ∠a = 180° − 115° = 65°. Final answer: ∠a = 65°. Answer: 65°

Correct answer: 65°

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