Two pipes can fill a cistern in 14 and 16 h, respectively. The pipes are opened simultaneously and it is found that due to leakage in the bottom, it took 92 min more to fill the cistern. When the cistern is full, in what time will the leak empty it?

(?)² = ?13² + 28 / 4 - (3)³ + 107
= ?169 + 7 - 27 + 107
= ?256
= ?16
= 4

Let A takes x and B takes 3N days to finish the job.
According to the question,
3N - N = 30
? N = 30/2 = 15 days
? B's time to complete the work = 3N
= 3 x 15 = 45 days

? (A + B)'s 1 day's work
= (1/15) + (1/45) = (3 + 1)/45 = 4/45
? (A + B) will finish the work in 4/45 days
? Required time = 4/45 = 11¹/₄

Let 75% of 480 = A x 15.
? (75 x 480)/100 = 15A
? A = (75 x 480)/ (100 x 15) = 24

Given, downstream speed = 9 km/h
and upstream speed = 5 km/h

According to the formula
Ravi's speed in still water = (Speed downstream + Speed upstream )/2
= 1/2(9 + 5) = 14/2 = 7 km/h
and speed of current = (Speed downstream - Speed upstream)/2
= (9 - 5)/2 = 4/2 = 2 km/h.

Part filled by X in 1st min and Y in the 2nd min = ( 1/6 + 1/7) = 13/42
Part filled by ( X + Y ) working alternately in 6 min = 1/2 x 13/42 x 6 =13/14
? Remaining Part = ( 1- 13/14 ) = 1/14
Now, it is the turn of X, one-sixth part is filled in 1 min.
One-fourteenth part is filled in (6 x 1/14) min = 3/7
? Required time = ( 6 + 3/7 ) = 6³/₇ min

Time taken by A to fill the tank, m = 15 min
? Time taken by B to fill the tank, n = 15 x 4 = 60
? Required time taken m x n/(m + n)
= (15 x 60)/(15 + 60) = (15 x 60)/75 = 12 min