Pipes and Pipe Dreams!


"If a narrow pipe fills up a cistern in 40 minutes and a wide pipe fills up the cistern in 20 minutes, how long will it take for both the pipes together to fill up the cistern?" Questions of this kind in school always had the effect of leaving my head swimming.

After finishing school, I thought pipes had passed out of my life. But, no! That was only a pipe dream. The pipes made their appearance in aptitude questions later in life.

After crossing that stage of life also, I was sure pipes will not trouble me anymore. That, again, was wishful thinking.

Before leaving for work every day, I have to fill a water storage tank. The narrow pipe I use for the purpose takes a long time to fill the tank. I got a wider pipe, and things brightened up for me.

All this talk about pipes has once again brought to mind the questions that tormented me in school. My question is: The wide pipe fills up the tank three times as fast as the narrow one. Both the pipes together fill up the tank in 40 minutes. How long does the narrow pipe take to fill up the tank all on its own?

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  • Union Public Service Commission - www.upsc.gov.in
  • IIT-Kharagpur - www.iitkgp.ac.in
  • Indian Statistical Institute - www.isical.ac.in
  • Indian Institute of Technology Madras - www.iitm.ac.in
  • Indian Institute of Management, Ahmedabad - www.iimahd.ernet.in
  • Indian Institute of Mass Commission - www.iimc.nic.in
  • IIT Bombay - www.iitb.ac.in
  • Indian School of Mines, Dhanbad - www.ismdhanbad.ac.in
  • Birla Institute of Technology, Ranchi - www.bitmesra.ac.in
  • Central Institute of Fisheries Nautical and Engineering Training - www.cifnet.nic.in
  • Indian Institute of Information Technology, Allahabad (Deemed University) - www.iiita.ac.in
  • Central Marine Fisheries Research Institute, Kochi - www.cmfri.com
  • Tata Institute of Social Sciences, Mumbai - www.tiss.edu