Q147
ArithmeticGeometry & Mensuration
An arc of length 121 cm makes an angle of $77^\circ$ at the centre of a circle. The radius of the circle is
- a.110 cm
- b.100 cm
- c.90 cm
- d.70 cm
Answer: (C) 90 cm
Using arc length $= r\theta$ (with $\theta$ in radians): $\theta = 77^\circ = \dfrac{77\pi}{180}$ rad, so $r = \dfrac{121 \times 180}{77\pi} = \dfrac{121 \times 180 \times 7}{77 \times 22} = 90$ cm.