A, B and C can do a piece of work in 7 days, 14 days and 28 days respectively. How long will they taken, if all the three work together? Choose the most appropriate option:
A) 4  B) 3  C) 5  D) 2  E) 1
1/7 + 1/14 + 1/28 = 7/28 = 1/4 =&gt; 4 days   4NSWER 4
<result>A</result>
A, B and C can do a piece of work in 7 days, 14 days and 28 days respectively. How long will they taken, if all the three work together?