Senior Manager
Joined: 07 Apr 2014
Status:Math is psycho-logical
Posts: 388
Location: Netherlands
GMAT Date: 02-11-2015
WE:Psychology and Counseling (Other)
M10-28
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21 Jan 2015, 01:40
I guess it needs less math thinking than rational thinking. Hope I will explain well enough. Let's put the information we have together:
Radius of front wheel: r
Radius of rear wheel: 2r
This means that when the front wheel makes 1 whole revolution, the rear one makes 2. That because its diameter (2 radii) is twice as large, so it covers twice the distance of the front wheel at the same time (if the weels were not attached, when the front wheel covers 5 meters, the back would cover 10). Put differently, since the wheels are actually attached to the same vehicle, the distance the rear wheel has covered in the same amount of time with the front is half the distance of the front (if the front wheel covered 10 meters, the read wheel covered 5).
Now, we know that the circumference is 1 meter (so, in 1 meter the cart makes 1 revolution) and that the cart covered 1
km.
In others words:
1 revolution in 1 meter
x revolutions in 1000 meters?
x = 1000 for the front wheel, so x = 500 for the rear wheel.