Pipe A can fill a tank in 6 hours. Due to a leak at the bottom, it takes 10 hours for the pipe A to fill the tank. In what time can the leak alone empty the full tank?  Choose one:
A) 13
B) 17
C) 15
D) 19
E) 12
Let the leak can empty the full tank in x hours 1/6 - 1/x = 1/10   =&gt; 1/x = 1/6 - 1/10 = (5 - 3)/30 = 2/30 = 1/15   =&gt; x = 15.   Answer: 15
<result>C</result>
Pipe A can fill a tank in 6 hours. Due to a leak at the bottom, it takes 10 hours for the pipe A to fill the tank. In what time can the leak alone empty the full tank?