IBM Research | Ponder This | November 2003 challenges

# Ponder This

## November 2003

<<October November December>>

Ponder This Challenge:

This puzzle is adapted from one published by S. B. Gashkov. The updated version is due to Sasha Ravsky, Gyozo Nagy, Gabor Sagi and the puzzlemaster.

Give the exact value for s, and an approximation correct to three decimal places, making the following statements true; provide justification for both the upper and lower bounds.

P is a regular pentagon one meter on each side. Consider a curve C of
some specified length T, lying within P, containing no straight line segments.
For any curve whose length T exceeds s, there is a straight line that intersects
the curve at least six times. But for any T less than s, there is a curve of
length T such that any straight line hits it at most five times.

We will post the names of those who submit a correct, original solution! If you don't want your name posted then please include such a statement in your submission!

We invite visitors to our website to submit an elegant solution. Send your submission to the ponder@il.ibm.com.

If you have any problems you think we might enjoy, please send them in. All replies should be sent to: ponder@il.ibm.com

Challenge: 11/03/03 @ 01:00 PM ET
Solution: 11/30/03 @ 01:00 PM ET
List Updated:

Dan Dima (11.6.2003 @08:53:00 AM EDT)

Michael Brand (11.7.2003 @03:21:02 AM EDT)
Alan O'Donnell (11.7.2003 @07:19:57 AM EDT)
Vladimir Sedach (11.7.2003 @01:21:06 PM EDT)
Graeme McRae (11.7.2003 @07:56:58 PM EDT)
Sarang Aravamuthan (11.7.2003 @07:34:30 PM EDT)
Alex Wagner (11.11.2003 @01:19:00 PM EDT)
R. Nandakumar (11.15.2003 @04:34:06 AM EDT)
Hagen von Eitzen (11.17.2003 @10:57:27 AM EDT)
John Ritson (11.19.2003 @11:52:18 PM EDT)
Steve Plate (11.20.2003 @01:02:11 AM EDT)
Niraj Jha (11.21.2003 @12:30:54 AM EDT)
Daniel Bitin (11.30.2003 @12:40:08 PM EDT)

Attention: If your name is posted here and you wish it removed please send email to the ponder@il.ibm.com.