A tank is to be filled completely with water for which 8 pipes of the same kind are used. The tank gets filled in 1 hour and 40 minutes. If 10 pipes of the same kind, as mentioned above, are used, in how much time (in hours and minutes) will the tank be completely filled?

A tank is to be filled completely with water for which 8 pipes of the same kind are used. The tank gets filled in 1 hour and 40 minutes.

It means that 8 pipes of the same efficiency can fill the tank in 1 hour 40 minutes (100 minutes). [1 hour =  60 minutes]
If 10 pipes of the same kind, as mentioned above, are used, then the time tank to be completely filled is 'y'.

$$8\times100 = 10\times y$$

$$800 = 10y$$

y = 80 minutes

As we know 1 hour = 60 minutes, so 80 minutes = 1 hour 20 minutes