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An express train is running between two stations with a uniform speed. If the diameter of each wheel of the train is 42 cm and each wheel makes 1200 revolutions per minute, find the speed of the train.

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#### Solution

radius of the wheel = `42/2` = 21 cm

Circumference of the wheel = 2π x 21 = 132 cm

Distance travelled in one minute

= 132 x 1200

= 158400 cm

= 1.584 km

Hence the speed of the train

= `[1.584 "km"]/[1/60"hr"]`

= 95.04 km/hr.

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