Three fill pipes A, B and C can fill separately a cistern in 3, 4 and 6 minutes respectively. A was opened first. After 1 minute, B was opened and after 2 minutes from the start of A, C was also opened. Find the time when the cistern will be full ?
Select:  A) 2 1⁄9 min.  B) 4 1⁄2 min.  C) 3 3⁄4 min.  D) 3 min.  E) None of these
Let cistern will be full in x min. Then,   part filled by A in x min + part filled by B in (x – 1) min + part filled by C in (x – 2)min = 1   ⇒ x/3+x−1/4+x−2/6=1   ⇒ 9x = 19 ⇒ x = 19⁄9 = 21⁄9 min.   2 1⁄9 min.nswer 2 1⁄9 min.
<result>A</result>
Three fill pipes A, B and C can fill separately a cistern in 3, 4 and 6 minutes respectively. A was opened first. After 1 minute, B was opened and after 2 minutes from the start of A, C was also opened. Find the time when the cistern will be full ?