Q&A #2647

Teachers' Lounge Discussion: Decimal manipulatives

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From: Pat Ballew 
To: Teacher2Teacher Public Discussion
Date: 2000113014:45:23
Subject: A method using conversion to fractions

  There are many ways to multiply decimals, but here is one way that
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
3) now convert back to decimals, 4945/100,000 = .04945

Notice that it is almost like using whole numbers.  Simon Stevin, the
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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