Answers

2014-08-18T20:28:37+08:00
 \frac{3}{4} →after 1 hour

 \frac{1}{3} →after 2 hours 

So,
 \frac{3}{4}- \frac{1}{3}   \\  \\ = \frac{9-4}{12}  \\  \\ = \frac{5}{12}
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