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Teachers' Lounge Discussion: Teaching percents

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From: Becky

To: Teacher2Teacher Public Discussion
Date: 1999022521:47:29
Subject: Foolproof way to learn percentages

My father was a principal and math teacher for 43 years and he made
all of his children memorize this basic sentence.   It sounds really
silly, but once you understand it you can manipulate any percentage
problem as long as you have two numbers to work with.  It worked for
him and four generations of children that he taught.  Here goes:  "If
both numbers are on the same side of the equal sign, you multiply.  If
not, you divide IS by OF.

Translated, for example:

11 is __% of 55.  The word IS means "equal sign".  Since both numbers
that we have are NOT on the same side of the "equal sign" you know
that you must do division.  To divide, you divide the number which is
closest to the word IS by the number closest to the word OF.  In this
case, you divide 11 by 55 and the answer is .20 or 20%.  

or... 20% of 55 is ___.  Are both numbers on the same side of the
"equal sign" (IS)?  The answer is yes so you multiply them.  55 x .20 
equals 11!

I learned this as a child and have never forgotten it and ALWAYS use
this formula whenever I have to figure percentages.  It has never
steered me wrong.  Try it!

I am proud to make this contribution to math understanding in memory
of Dad, Raymond Giroud, who passed away at 87 on Oct. 27, 1997.
Thank you for everything, Dad.  I love you!

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