A sector cut from a circle of radius 7 cm has area $38.5{\text{cm}}^2$. Find its central angle in degrees. Take π = 22/7.

The whole circle has area $(22/7)\times 49=154{\text{cm}}^2$, and 38.5 is exactly one quarter of 154. A quarter of a full turn is 90°. (Comparing 38.5 with the circumference, 44 cm, instead of with the area is the standard trap — it sets a length against an area.)