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 correct choice from the following answers
A) 4 days	B) 3 days	C) 6 days	D) 8 days	E) 9 days
4 days   4 days   1/7 + 1/14 + 1/28 = 7/28 = 1/4 =&gt; 4 days
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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?