Gate Exam Numerical Ability Area and Volume

Two pipes – A and B – can fill a cistern in 20 min and 30 min respectively. A tap C can empty the cistern in 25 min. If A, B and C are opened in that order with a time gap of 2 minutes each, how long will it take for the cistern to be full?

a.18+2/3
b.20+12/13
c.16+12/13
d.none

Read Solution (Total 2)

b is correct.
10 years agoHelpfull: Yes(1) No(3)

Rate of flows:
Pipe A = 1/20
Pipe B = 1/30
Pipe C = 1/25 (used for emptying so -1/25)
now the order timeline for opening of pipes and tap are as follows:
[A] ---(2min)----> [B] ----(2min)---> [C] ------(T)------> FullCistern
So,
(T+4)/20 + (T+2)/30 - T/25 = 1
:: T= 16 12/13
Option C is correct
10 years agoHelpfull: Yes(1) No(1)

Gate Other Question

A picnic invites two kinds of charges: bus fare, which is independent of the number of people attending the picnic and buffet lunch, which increases directly with an increase in the number of people. The charges are calculated to be Rs. 165 per head when there are 200 invitees and Rs. 170 per head when there are 150 invitees. What would be the charges per head when there are 100 invitees? Q. A and B can do a piece of work in 18 and 9daysrespectively. A does the work for a few days andleft, then B continued for 6 days. How many daysdid A and B work together