math
posted by vincent .
One wheel has a diameter of 30 inches and a second wheel has a diameter of 20 inches. The first wheel traveled a certain distance in 240 revolutions. In how many revolutions did the second wheel travel the same distance?
not just an answer please
A.120
B.160
C.360
D.420
E.480

math 
Reiny
short way:
the number of revolutions varies inversely with the diameter of the wheel
i.e. the larger the wheel the smaller the number of revs.
R1/R2 = C2/C1
240/R2 = 20/30
20R2 = 7200
R2 = 360
or
distance covered by first wheel = 2π(15)(240) = 7200π inches
circumference of 2nd wheel = 2π(10) = 20π inches
for the same distance of 7200π inches
number of revolutions = 7200π/(20π) = 360 revs 
math 
Dominique
c.360
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