June 2013








Solution

I think there should be 22 steps. What do think?

This is how I worked it out:

I had climbed down seven steps when the boy starts.

After that I climb down a further number of steps (let this number be "x") when the boy reaches the top.

I have yet to climb down four more stairs.

Therefore, the total number of stairs is: 7 + x + 4, or 11 + x.

The boy takes two steps at a time. So when I have taken "x" steps, he has climbed up 2x number of steps and reached the top. Therefore, the total number of steps is 2x.

Thus, 11 + x = 2x.

Thus, x = 11.

The total number of steps is 2x. Substitute x = 11, and we have the total number of steps as 22.



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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

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