Question

A pipe can fill a cistern in 12 min and another pipe can fill it in 15 min, but a third pipe can empty it in 6 min. The first two pipes are kept open for 5 min in the beginning and then the third pipe is also opened. Time taken to empty the cistern is​

Answer 1

Answer:

According to the question,

x6−x+512−x+512=0

x6−x12−512−x15−515=0

x6−x12−x15=512+515

10x−5x−4x60=25+2060

x60=4560=x=45min.