Question

5 and 6 hours
(0) +0 uuu
18. Pipes A and B can fill a tank in 5 and 6
respectively. Pipe C can empty it in 12 hours
The tank is half full. All the three pipes are
operation simultaneously. After how much time
will the tank will be full.​

Answer 1

Use harmonic mean to solve this type of questions,,
To fill or empty it is same. therefore when three pipes fill the tank simultaneously, it takes 3/[(1/a)+(1/b)+(1/c)]
=>3/[(1/5)+(1/6)+(1/12)]=3/[(12+10+5)/60]
=>3*60/27=60/9=20/3=6.66,, we required half tank to fill, therefore 20/6=3.333 or 6.66/2=3.333. Therefore it takes 3.33hours!!