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Q&A #2647

Teachers' Lounge Discussion: Decimal manipulatives

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From: Pat Ballew 
To: Teacher2Teacher Public Discussion
Date: 2000113015:45:23
Subject: A method using conversion to fractions

Sarah,
  There are many ways to multiply decimals, but here is one way that
will
help you understand what you are doing.

1)  convert both decimals to a fractions (proper or improper)
2)  Multiply the fractions in the usual way, multiply the numerators,
multiply the denominators
3)  Convert the answer back to decimals

Example :  Multiply .23 * .215

1)  convert to 23/100 times 215/1000
2)  multiply 23 * 215 for the numerator (4945)  and 100*1,000=100,000
for the
denominator...
3) now convert back to decimals, 4945/100,000 = .04945

Notice that it is almost like using whole numbers.  Simon Stevin, the
Dutch
mathematician/Engineer who first made decimals popular in European
mathematics, never thought of them as fractions at all.

Good luck

 -Pat Ballew, for the T2T service


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