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Conference rusure::math

Title:Mathematics at DEC
Moderator:RUSURE::EDP
Created:Mon Feb 03 1986
Last Modified:Fri Jun 06 1997
Last Successful Update:Fri Jun 06 1997
Number of topics:2083
Total number of notes:14613

1553.0. "Balanced Products" by CADSYS::COOPER (Topher Cooper) Fri Jan 31 1992 13:00

From: [email protected] (Robert D. Silverman)
Newsgroups: sci.math
Subject: Elementary (counter-intuitive) Puzzle
Message-ID: <[email protected]>
Date: 29 Jan 92 18:38:19 GMT
Sender: [email protected] (News Service)
Organization: Research Computer Facility, MITRE Corporation, Bedford, MA


Here's a cute puzzle I've been toying with. The answer (at least to me)
was surprisingly counter-intutive.

Consider the set of integers. What fraction of them can be written as a*b
(a,b not necessarily prime) where a and b are nearly equal. I define
'nearly equal' to mean that   b/2 <= a <= 2b. In other words, a and b
are within a factor of 2 of one another.
 
In other words, what is the density of integers N = ab such that
b/2 <= a <= 2b.

The answer surprised me in that

(a) It turned out to have positive density
(b) It was rather high. 

Maybe I shouldn't have been surprised.

--
Bob Silverman
These are my opinions and not MITRE's.
Mitre Corporation, Bedford, MA 01730
"You can lead a horse's ass to knowledge, but you can't make him think"
T.RTitleUserPersonal
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1553.1fractions are easy...CIVAGE::LYNNLynn Yarbrough @WNP DTN 427-5663Fri Jan 31 1992 13:291
It's not stated, but I think the proposer assumes a and b are also integers.