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Path: utzoo!linus!philabs!seismo!rlgvax!cvl!umcp-cs!james
From: james@umcp-cs.UUCP
Newsgroups: net.math
Subject: Re: Math for Smart Alecks
Message-ID: <4908@umcp-cs.UUCP>
Date: Sat, 28-Jan-84 18:00:23 EST
Article-I.D.: umcp-cs.4908
Posted: Sat Jan 28 18:00:23 1984
Date-Received: Tue, 31-Jan-84 03:47:32 EST
Organization: Univ. of Maryland, Computer Science Dept.
Lines: 13

Yes, it works.  Think of it this way: you start with two numbers, whose
product you are going to construct.  I'll call these numbers A and B.
A*B is "A groups of B".  If A is even, that is "A/2 groups of 2B", so
you can see that anytime you halve the left number and double the right
number, their product is equal to the product of the numbers immediately
above them (in your columns).  This means you should scratch out the numbers
above them IN THIS CASE, WHEN the previous A was even!

When the left number is odd, A * B == (A-1)/2 * 2B  +  B, so you need that
extra B immediately above the new 2B in the DOUBLES column, to allow
for the remainder you ignored when halving A.

  --Jim