JAMB Mathematics 2021 Objective — Question 17

Question 17 of 40 from the Joint Admissions and Matriculation Board (JAMB) Mathematics 2021 Objective paper, with the correct answer and a full explanation.

17. Four interior angles of a pentagon are (90 - x)°, (110 - 2x)°, (90 + x)°, (110 + 2x)°. Find the fifth interior angle (a) 140° (b) 130° (c) 120° (d) 110°

A. 140°Correct
B. 130°
C. 120°
D. 110°

Explanation

Sum of interior angles of a pentagon = (5-2) × 180° = 540°. The four given angles sum to 400° (the x terms cancel), so the fifth angle = 540° - 400° = 140°.

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