A bath can be filled by the cold water pipe in 10 min and by hot water pipe in 15 min (independently each). A person leaves the bathroom after turning on both pipes simultaneously and returns at the moments when the bath should be full. Finding, however, that the waste pipe has been open he now closes it. In 4 min more, bath is full. In what time would be the waste pipe empty it?

A.

9 min

B.

12 min

C.

15 min

D.

14 min

• Lets assume some time l.c.m(10, 15)min=30 min
  Now in 30 min time cold water pipe will fill the bath 30/10=3 times whereas hot water pipe will fill it 30/15=2 times.
  
  So in 30 min time bath will be filled 3+2=5 times.
  
  So ,emptied bath will be fully filled in 30/5=6 min time if waste pipe is closed.
  
  Initially waste pipe is opened, after 6 mins is passed and waste pipe is closed it takes 4 more minutes to fill the bath fully.
  
  so waste pipe has emptied the 4/6=2/3 part of bath in 6 mins.
  Rest 1/3 part of tank can be emptied by the waste pipe in 6/2=3 mins.
  
  So waste pipe would empty the tank in 6+3=9 min
• 9 years agoHelpfull: Yes(0) No(2)