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?

Diameter of wheel = 80 cm
Radius of wheel (r) = 40 cm
Circumference of wheel = 2πr = 2π (40) = 80m cm
Speed of car = 66 km/hour = (66 × 10000)/60 cm/min = 110000 cm/min
Distance travelled in 10 minutes = 110000 x 10 1100000 cm
Let the wheel makes n revolutions in 10 minutes. Therefore,
n × Distance travelled in one revolution (circumference) = Distance travelled in 10 minutes
⇒ n × 80π = 1100000
⇒ n = (1100000)/80π = (1100000 x 7)/(80 x 22) = (35000)/8 = 4375
Hence, the wheel takes 4375 revolutions in 10 minutes.

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