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Fractions and Rational Numbers
Concepts and Definitions
Copyright © 2013 by Lynda Aguirre 1
Definitions
Numerator: The top number (how many pieces YOU have)
Denominator: The bottom number (how many pieces make up a Whole object-or the size of the pieces)
Copyright © 2013 by Lynda Aguirre 2
Are the following Rational numbers or Fractions or Both?
both bothfraction
bothfraction fraction
= 2
Copyright © 2013 by Lynda Aguirre 3
Ratios vs. Fractions
Ratios were used by the Greeks who did not have fractions.
Ratio: 2 boys to 3 girls
The format we use for fractions today is thought to have been introduced By the Hindus
and the bar introduced by the Arabs.
Copyright © 2013 by Lynda Aguirre 4
Represent the fraction using the following methods:A.pictorially B.number line C.area modelsD.ratio algebra problemE.Ratio—parts and wholes
Copyright © 2013 by Lynda Aguirre 5
Wholes and Parts-changing forms
What part of the day is 6 hours?
We assume the student knows there are 24 hours are in a day
We also assume the student knows how to reduce fractions
1:4
Copyright © 2013 by Lynda Aguirre 6
What part of an hour is 20 minutes?
We assume the student knows there are 60 minutes in an hour
We again assume the student knows how to reduce fractions
1:3
Wholes and Parts-changing forms
Copyright © 2013 by Lynda Aguirre 7
Equivalent fractions
Unit fractions have a “1” on the top.
The instructions will often want fractions converted to another form that has the same value as the original.
Equivalent fractions have equal values or represent the same amount of the whole.
Simplest form fractions have been reduced to the smallest possible value(or are relatively prime)
Copyright © 2013 by Lynda Aguirre 8
Method: Calculating equivalent fractions
Equivalent fractions
Multiply the top and bottom by the same number (this is the reverse process to reducing)
This process can be done with any numbers, it doesn’t have to be 2 and 3
Copyright © 2013 by Lynda Aguirre 9
Changing to a specific equivalent fraction
If a specific equivalent fraction is desired, you will set up the problem as analgebraic equivalence relation (i.e. two fractions with an equal sign between them).
The unknown piece will be represented by a variable (x, y, etc.)
Copyright © 2013 by Lynda Aguirre 10
Process: Cross-Multiplication
Copyright © 2013 by Lynda Aguirre 11
Cross Multiplication-practice
Copyright © 2013 by Lynda Aguirre 12
Change into Unit FractionsA Unit Fraction is a special equivalence relation where
the new fraction has a numerator of “1”.This makes the new denominator your unknown variable (or “x”).
Use cross-multiplication to find unit fractions for the values below
Note: These answers oftencome out as fractions
or decimals
Copyright © 2013 by Lynda Aguirre 13