There are three bulbs on the 3rd floor and there are three switches X, Y and Z on the first floor. Each switch belongs to one bulb, not necessarily in order. You can switch on or off as many times you want to but you can go on the 3rd floor only once. How will you find out which switch belongs to which bulb?
Note: You are the only person over there. You can’t go outside and can’t use any tools.
November Solution
Switch on the switch X and wait for 20 minutes, then turn it off. Now turn on switch Y and go up to the 3rd floor. The bulb, which is hot but not lit, corresponds to switch X. The bulb, which is lit, corresponds to switch Y. The third bulb, which is not lit and is cold, corresponds to switch Z.
The correct responses were sent by:
Dustin W. Qualls, P.E., PTOE Traffic Engineers, Inc.
Jose J. Asyn, P.E. Fugro Consultants. Inc.
Todd Greer Fugro Consultants, Inc. / University of Houston
Michael Kane, P.E. TCB
December Problem
A frog starts climbing a 15-foot wall. Each hour he climbs 3 feet and rests for 30 minutes. During rest, he slips back 2 feet. How many hours does the frog take to reach the top?
Send your solutions to Kishore Juluru at kjuluru@etsiteam.com. Please include “ASCE Puzzle - December ” in the email subject. All correct responses will be recognized in the January issue.
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