# 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?

The diameter of the wheel of the car = 80 cm

Radius (r) of the wheel of the car = 40 cm

Circumference of wheel = 2πr

⇒ 2π (40) = 80π cm

Speed of car = 66 km/hour

1 km = 1000 m and 1m = 100 cm
⇒ 1 km = 100000 cm

= 110000 cm/min
As distance= speed × time

Distance traveled by car in 10 minutes

= 110000 × 10
= 1100000 cm

Let the number of revolutions of the wheel of the car be "n".

n × Distance travelled in 1 revolution (i.e., circumference)
(In one revolution of the wheel, a wheel covers the distance equal to its circumference)

= Distance travelled in 10 minutes

n × 80 π = 1100000

n =

=

= 4375

Therefore, each wheel of the car will make 4375 revolutions.

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