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JAMB Mathematics 1980 Question 26

Question 26

Angles and Polygons

A pentagon has four of its angles equal. If the size of the fifth angle is 60°, find the size of each of the four equal angles.

  1. A.60°
  2. B.108°
  3. C.120°
  4. D.150°
  5. E.None of the above.
Show the answer and explanation

Answer: C (120°)

Explanation

The angles of a pentagon add up to (5 − 2) × 180° = 540°. 540° − 60° = 480°, shared by four angles: 120° each.