Latest CAT Aptitude Question SOLUTION: A cistern has 3 pipes A,B and C. A and B can fill the tank in 15 and 18 minutes respectively whereas all three simultaneously take 45 minutes. Let flow of water in every pipe chang

• Placement Papers
• /
• CAT
• /
• Numerical Ability
• /
• Time and Work

CAT Question Papers:

(#M40136773) CAT Numerical Ability question Keep an EYE

A cistern has 3 pipes A,B and C. A and B can fill the tank in 15 and 18 minutes respectively whereas all three simultaneously take 45 minutes. Let flow of water in every pipe change directions for two minutes after every five minutes of regular flow,beginning with regular flow. How much time will now be taken to fill the empty tank?

Asked In CAT Harsh Bihani (9 years ago)

Unsolved Read Solution (2)

Is this Puzzle helpful?   (2)   (1) Submit Your Solution Time and Work

Read Solution (2) :

Naresh Nani  (7 years ago)

A takes = 15 min to fill the tank , so in 1 min =1/15, 5 min = 5/15
B " = 18 min , 1 min =1/18, 5 min =5/18
now calculate for C,
1/A+1/B+1/C=1/45 => 1/15+1/18+1/c=1/45, solving we get C= -0.1
what is its mean -0.1, it means C doing -ve work w.r.t A & B.
C takes 10min to empty the tank , in 1 min -0.1 5 min= -0.5

So, in 5 min (A+B+C) =10/90 wk,
now its turn for reverse 2 min wk = 4/90 (approx.)
it means in 7 min wk= 11/90-4-90=6/90
7min---------6/90
x-------------1 full tank
solving for x.x=(90*7)/6
total time = 105 min is correct ans

Is this solution Helpfull? Yes (1) | No   

vipul kumar  (8 years ago)

Ans: 108 min.
Basically u can assume that A,B,C are 3 persons for convenience.
A takes = 15 min for 100% work , so in 1 min =100/15= 6.66%, 2 min= 13.32%, 5 min = 33.30% work
B " = 18 min " " , 1 min =100/18= 5.55%, 2 min= 11.10%, 5 min = 27.75% work
now calculate for C,
1/A+1/B+1/C=1/45 => 1/15+1/18+1/c=1/45, solving we get C= -10% ??
what is its mean -10%, it means C doing -ve work w.r.t A & B.
C takes -100% work in 10min, in 1 min -10%, in 2 min = -20%, in 5 min= -50%

So, in 5 min (A+B+C) = 11% wk,
now its turn for reverse 2 min wk = (-4.5%) (approx.)
it means in 7 min wk= 11-4.5 = 6.5%
so, in 7*15 min wk = 6.5*15 = 97.5 % (rem = 100%-97.5= 2.5%)
in next 2-3 min he will do rem 2.5 % work
total time = 7*15+ 2.5min= 107.5 or 108 min .......:-)

Is this solution Helpfull? Yes | No   

Please Login to Read Solution.