math  please help
posted by Nilan on .
What is the rotational speed (rpm) of the 64 in diameter rear tires of a tractor traveling at 6.5 mph if there is no slippage?
How do I work this?
Thank you.

radius = 32 in = 2.67 ft
circumference = 2 pi r = 16.76 ft
how many feet in a minute?
6.5 mile/hr * 5280 ft/mile * 1 hr/60 min
=550 ft/min
so how many circumferences/min?
550/16.76 = 32.8 revs/min