Question

Pipe A can fill a pool in 15 minutes and pipe B alone can do it in 10 mibutes. Both the pipe are opened after 4 minutes water from pipe B stop flowing.In how much time will pipe A fill the part of the pool

Answer 1

let 1= total job
rate=job/min
for A=the rate is 1/15
for B= the rate is 1/10
at 4 minutes both were open..so the part of the job done is..
(1/15+1/10)X 4min= 2/3
but after 4 min pipe B closed so A has to work alone...then
(1/15)(x)
where x is the time..adding both and equate it to the total work done
2/3 + x/15 = 1
finding for x
x= 5 minutes..

Answer 2

rate of pipe A = 1/15
rate of pipe B = 1/10
combined rate = 1/6

amount done after 4 minutes = 4(1/6) = 2/3
so 1/3 is left to be done

time using only A
= (2/3) / (1/15)
= 10 minutes

Answer 3

its 5
if 1/3 is left and using a then.

1/3=(1/15)x
x=5

Answer 4

Thanks nms for catching my error
I used 2/3 instead of 1/3

(I must have looked back at the wrong fraction)