Circular gears L and R start to rotate at the same time at the same rate. Gear L makes 10 complete revolutions per minute and gear R makes 30 revolutions per minute. How many seconds after the gears start to rotate will gear R have made exactly 6 more revolutions than gear L?
Choose the correct choice from the following choices.
A) a) 6 B) b) 8 C) c) 10 D) d) 12 E) e) 18
Gear L -- 10 rotations per 60 seconds -- 1 rotation per 6 seconds.   Gear R -- 40 rotations per 60 seconds -- 3 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.   Answer: e) 18
<result>E</result>
Circular gears L and R start to rotate at the same time at the same rate. Gear L makes 10 complete revolutions per minute and gear R makes 30 revolutions per minute. How many seconds after the gears start to rotate will gear R have made exactly 6 more revolutions than gear L?