Q&A #17351

Teachers' Lounge Discussion: alternative ways to mulitply

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From: Loyd

To: Teacher2Teacher Public Discussion
Date: 2010111218:11:00
Subject: Re: bow tie multiplication

If you are going go one in algebra, and higher math, then we should
stick to the methods that are more universal.  

For example, lets works 23 x 45 by the distributive method:

(20 + 3)(40+5).  Distribute the (20+3):

(20+3)40 + (20+3)5
40(20+3) +5(20+3) distribute the 40 and the 5:

40x20+40x3 +5x20+5x3

Of course we would have worked this problem by the FOIL method.  But
if there was three terms in the problem such as:
(a+b+c)(d+e+f) we would use the distributive property such as:

a(d+e+f)+b(d+e+f)+c(d+e+f) and continue with the distributive
property.  FOIL and the Lincoln method wouldn't work for the three
term problems.  But they are OK for the two term problems. That is
something like the criss cross method some teachers use.  It works
sometimes but not for all problems. 

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