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 60 revolutions per minute. How many seconds after the gears start to rotate will gear R have made exactly 8 more revolutions than gear L? Answers
A) a) 6
B) b) 8
C) c) 10
D) d) 14
E) e) 12
Gear L -- 20 rotations per 60 seconds -- 2 rotation per 6 seconds.   Gear R -- 60 rotations per 60 seconds -- 6 rotations per 6 seconds.   First 6 seconds -- Gear L makes 1 rotation. -- Gear R makes 4 rotations -- Net difference -- 4 rotations   Hence every 6 seconds the difference between the number of rotations of R and L gear is 4 units.   Required net difference should be 8 rotations =&gt; 2 (6 seconds later) ==&gt; 12 seconds.   Answer: e) 12
<result>E</result>
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 60 revolutions per minute. How many seconds after the gears start to rotate will gear R have made exactly 8 more revolutions than gear L?