Question

Two pipes a andb can gil a tank in 36 min. And 45 min. Respectively. A water pipe c can emptythe tank in 30 min. First a and b are opened. After 7 minutes, c is alsoopened. In how much time, the tank is full ?

Answer 1

(A + B)'s 7 minutes filling =(5+4)×7=63 units  

Remaining capacity =180−63=117 units  

Now C is opened, it empties by 6 units/min.  

So total units filled in tank is =(5+4)−6=3 units/min  

Now tank can be filled in   =1173=39min

Tank is filled up in  = 7+39 minutes=46 min