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?

Let us given that, 

The diameter of the wheel of the car = 80 cm

Thus, The  radius = Diameter / 2

= 80/2 

= 40 cm

We know that, The distance tavelled by the wheel in one revolution is the circumference of the wheel.

Circumference of the wheel = 2$\mathrm{\pi }$r 

= 2 $\mathrm{\pi }$ (40)

= 80 $\mathrm{\pi }$

Hence, the distance traveled in one revolution = 80 $\mathrm{\pi }$

Given that, The speed of the car =  66 km per hour

= (66 $\times$ 100000) / 60

= 110000 cm /min

In 10 minutes, The distance traveled by the car = 110000 $\times$ 10

= 1100000 cm

consider, n be the number of revolutions of the wheel of the car

Thus we get,

Distance traveled in one revolution $\times$ n = Distance traveled in 10 min

 80$\mathrm{\pi }$  $\times$ n  = 1100000

n = (1100000 $\times$ 7) /( 22 $\times$80)

n = 35000/8

n = 4375

Hence, The number of revolutions of the wheel of the car = n = 4375