the radius of a truck tire is 21 inches. if it makes 7 rotations every second, in how many miles per hour is the truck moving?

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Calculate circumference of truck tire: 2 x pi x r = 2 x 3.14 x 21 = 131.88 inches Calculate distance travelled in a second(7 rotations = 7 times the circumference): 131.88 x 7 = 923.16 inches per second Convert inches per second to miles per hour: 923.16 inches x (1 ft / 12 inches) = 76.93 ft76.93 ft x (1 mile / 5280 feet) = 0.01457 miles(0.01457 miles/sec)(60 sec/min) =  0.8742 mi/min)(0.8742 mi/min)(60 min/hr) = 52 mph