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Q&A #6001


Reciprocals

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From: Marielouise (for Teacher2Teacher Service)
Date: Mar 22, 2001 at 16:08:06
Subject: Re: Reciprocals

Hi, Julie,

This is your lucky day. What i found is not exactly what you wished but you
could make it.  I was planning for a family math session today and opened
the Family Math book to:  "The Lost Number." (249).   This activity is to
practice pattern recognition and to reinforce  the understanding of inverse
relationships or reciprocals for multiplication.  In order to do this
activity you will need to have a calculator for each pair of children that 
has the "constant divide feature."

The text advises parents to practice before doing this with their child.  I
suggest that you do so also before using it with your class.   You can set
up the "constant divide" feature by pressing the divide key, then a number,
then the equal sign.   For example:  / 782 =  will set the calculator to 
divide by 782 any number that is entered into the calculator

GAME:
1. hide a number in each of the pair's calculator.
2. tell this story:

One day Aunt Bebe called all of the neighbor children together and told them
that she had just discovered that there was a number lost in her calculator.
She needed their help in finding out what the number might be. She said
the instructions that had come with the calculator said:  if a number gets 
lost, then
 enter a three digit number
 enter =
 write down the answer as this is a clue!
 continue to enter three digit numbers and = to collect clues.
 the three digit number that gives the answer of 1 is the LOST NUMBER.

It took Aunt Bebe ten guesses to find her number.  How many guesses do you
think it will take you to find the number lost in this calculator.

The Family Math book gave an example for the number 782.   The guesses were
123 = too small
100 = too small
999 = too big
888 = too big
777 = too small but closer than 123 and 100
788 = too big but closer than 888
780 = too small
785 = too big
782 = 1   the Lost Number.

This could be a chance to discuss what the clues told you. The exercise
could also help you talk about the reciprocal being equal to the number.

You mentioned that you had to help them change the number to a mixed number
or decimal. This game would encourage them to use decimals if you use 
decimals in putting in the number

-Marielouise, for the T2T service

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