Question 896203
let x be amount of revolution / sec.
radius of wheel = 13 inches
circumference = 2*pi*r = 2*pi*13 = 26pi inches ( linear distance one revolution of wheel can traveled)

one mile = 63360 inches
one hour = 3600 sec.
and bike is traveling at speed of 14 miles/hour = 887040 inches/hour = 887040 inches/ 3600 sec.

x = (887040 inches/ 3600 sec.)/(26pi inches) = 18.953846154 rev./sec.
x is roughly 19 rev./sec.

if you have alternative ways of solving it, i would love to hear from you. thank you
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