Two pipes A and B can fill cistern in 37 1/2 minutes and 45 minutes respectively. Both pipes are opened, the cistern will be filled just in half an hour, if the pipe B is turned off after?

Correct Answer: 9 minutes

2/75+1/45 =6+5/225

According to question,

cistern fills in 30 minutes

So pipe A worked for 30 minutes

It filled = 30×6=180units

Remaining capacity = 225−180 = 45 units

So this remaining capacity must be filled by B

B must have filled it in45/5=9min.