Math CentralQuandaries & Queries


Question from Al, a parent:

how many rpm does a 3.5 in. diameter wheel turn at 7 miles per hour

Hi Al,

The wheel has diameter 3.5 inches. What is its circumference in inches?

A point on the circumference of the wheel moves at 7 miles per hour. There are 5280 feet in a mile and 12 inches in a foot so 7 miles is $7 \times 5280 \times 12$ inches. Divide that by the circumference of the wheel to determine the number of revolutions there are in an hour. How many minutes are in an hour? How many revolutions are there in a minute?



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