HOTS Mathematics Primary 5 Angles

Siti is laying floor tiles against a straight wall MN. At point O on the wall, two grout lines create rays OA and OB on the same side of MN, forming three angles. Siti measures that angle MOA is 3/2 times angle BON, and angle AOB is 5/6 of angle MOA. What is angle MOA?

A 48°
B 60°
C 72°
D 90°
Show Worked Solution

Worked Solution

Step 1: Let angle BON = k. Then angle MOA = (3/2)k. angle AOB = (5/6) × (3/2)k = 5k/4. Step 2: Straight-line sum: (3k/2) + (5k/4) + k = 180 6k/4 + 5k/4 + 4k/4 = 180 15k/4 = 180 k = 48 Step 3: angle MOA = (3/2) × 48 = 72 Verify: 72 + 60 + 48 = 180 ✓

Correct answer: 72°

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