A, B and C can do a piece of work in 5 days, 10 days and 15 days respectively. How long will they taken, if all the three work together?	Pick one.
A) 2  B) 4  C) 2 8/11  D) 67  E) 9
1/5 + 1/10 + 1/15 = 11/30 =&gt; 30/11 =&gt; 2 8/11 days   Answer: 2 8/11
<result>C</result>
A, B and C can do a piece of work in 5 days, 10 days and 15 days respectively. How long will they taken, if all the three work together?