HOTS Mathematics Primary 5 Angles

Five rays OA, OB, OC, OD and OE all start from point O. Angles AOB, BOC, COD and DOE are all equal. Angle EOA = 40°. Find the size of angle BOD.

A 160°
B 80°
C 40°
D 320°
Show Worked Solution

Worked Solution

Step 1: Let each of the four equal angles be x°. The five angles at point O sum to 360°: 4x + 40 = 360 Step 2: Solve for x. 4x = 360 − 40 = 320 x = 320 ÷ 4 = 80° Step 3: Angle BOD spans two of the equal angles (angle BOC and angle COD). Angle BOD = x + x = 80 + 80 = 160° Answer: 160°

Correct answer: 160°

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