The wheels of a car are of diameter 80 cm each. How many complete revolutions does each wheel make in 10 minutes when the car is travelling at a speed of 66 km per hour?

Distance covered by the car in 10 minutes

\( = \ \frac{66 \ × \ 1000 \ × \ 100 \ × \ 10}{60} \) \( = \ \frac{6600000}{6} \) cm

Circumference of the wheel of the car

\( = \ (2 \ × \ \frac{22}{7} \ × \ 40) \)cm

∴ Number of revolutions in 10 minutes when the car is travelling at a speed of 66 km/hr.

\( = \ \frac{6600000}{6} \ × \ \frac{7}{2 \ × \ 22 \ × \ 40} \ = \ 4375 \)

Hence, the wheel of car makes 4375 revolutions in 10 minutes.