WAEC Mathematics 2018 Question 15

Question 15

Mensuration of Plane Shapes

A piece of thread of length 21.4 cm is used to form a sector of a circle of radius 4.2 cm on a piece of cloth. Calculate, correct to the nearest degree, the angle of the sector. [Take π = 22/7]

A.170°
B.177°
C.182°
D.192°

Show the answer and explanation

Answer: B (177°)

Explanation

Arc = 21.4 − 8.4 = 13 cm. θ/360 × 2 × 22/7 × 4.2 = 13 gives θ = 13 × 360/26.4 ≈ 177°.