Circular gears L and R start to rotate at the same time at the same rate. Gear L makes 20 complete revolutions per minute and gear R makes 40 revolutions per minute. How many seconds after the gears start to rotate will gear R have made exactly 6 more revolutions than gear L?
Answers:
A) a) 6  B) b) 8  C) c) 10  D) d) 12  E) e) 15
Gear L -- 20 rotations per 60 seconds -- 2 rotation per 6 seconds.   Gear R -- 40 rotations per 60 seconds -- 4 rotations per 6 seconds.   First 6 seconds -- Gear L makes 1 rotation. -- Gear R makes 4 rotations -- Net difference -- 2 rotations   Hence every 6 seconds the difference between the number of rotations of R and L gear is 2 units.   Required net difference should be 6 rotations =&gt; 3 (6 seconds later) ==&gt; 18 seconds.   a) 6nswer: a) 6
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Circular gears L and R start to rotate at the same time at the same rate. Gear L makes 20 complete revolutions per minute and gear R makes 40 revolutions per minute. How many seconds after the gears start to rotate will gear R have made exactly 6 more revolutions than gear L?