# math

An instrument shows the number of revolutions per
minute made by each tire of a car. In each revolution, the
car travels a distance equal to the circumference of one of
its tires. The circumference of each tire is equal to 2πr,
where r is the radius of the tire.
If the radius of each tire on Maria’s car is 0.30 meter,
what is the approximate speed of Maria’s car, to the
nearest kilometer per hour, when the instrument is
showing 779 revolutions per minute?
(1 kilometer = 1000 meters)

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1. tire circumference * rpm * minutes per hour / meters per km

2 * π * 0.30 * 779 * 60 / 1000

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posted by scott
2. C = 2pi*r = 6.28 * 0.3 = 1.884 m/rev. = Circumference.

Speed = 779rev/min * 1.884m/rev. * 1km/1000m * 60min/h = 88 km/h.

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posted by Henry

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