JAMB 1993 · UME · Q27

Calculate the length, in cm, of the arc of a circle of diameter 8 cm which subtends an angle of $22\frac12^\circ$ at the centre.

Worked solution (try it first)

The diameter is 8 cm, so the radius is 4 cm and the circumference is $2\pi \times 4 = 8\pi$ cm.
The arc is $\frac{22.5}{360} = \frac1{16}$ of the circle: $\frac1{16} \times 8\pi = \frac\pi2$ cm, option D.