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Subtracting Fractions

Subtracting Fractions. By: Greg Stark EC&I 831. Subtracting Fractions. As with adding, before fractions may be subtracted from one another, the pieces of the whole, the denominator, must be the same size.

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Subtracting Fractions

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  1. Subtracting Fractions By: Greg Stark EC&I 831

  2. Subtracting Fractions • As with adding, before fractions may be subtracted from one another, the pieces of the whole, the denominator, must be the same size • Fractions with the same denominator are called like fractions and can be subtracted from each other Represents the number of parts of a whole we have. Numerator -------------------- Denominator Represents the number of parts into which the whole has been divided

  3. Subtracting Like Fractions To subtract like fractions, subtract the numerators from each other in order and place the difference (answer) over the original denominator 2 4 3 - 2 4 1 4 3 4 - = =

  4. Subtracting Like Fractions Another example: 1 8 5 - 1 8 4 8 4 8 1 2 5 8 - = = = ÷ 4 ---- ÷ 4

  5. Subtracting fractions from a whole In order to subtract a fraction from a whole, we need to regroup one of the wholes (or “borrow”) 5 12 12 12 7 12 6 5 - Look at the denominator of the fraction that is being subtracted – in this case, 12ths This will be what we regroup the whole into so we will have like fractions 5

  6. Subtracting fractions from a whole Another example: In order to subtract a fraction from a whole, we need to regroup one of the wholes (or “borrow”) 1 3 3 3 2 3 3 4 - Look at the denominator of the fraction that is being subtracted – in this case, 3rds This will be what we regroup the whole into so we will have like fractions 3

  7. Subtracting unlike fractions As with adding, before fractions may be subtracted from one another, the pieces of the whole, the denominator, must be the same size The denominators of the fractions do not match – we must find the LCM of 4 and 6 – and make equivalent like fractions, before we subtract 7 12 3 4 2 12 9 12 1 6 - X 3 ---- X 3 X 2 ---- X 2 = - =

  8. Subtracting unlike fractions As with adding, before fractions may be subtracted from one another, the pieces of the whole, the denominator, must be the same size The denominators of the fractions do not match – we must find the LCM of 3 and 5 – and make equivalent like fractions, before we subtract 4 15 2 3 6 15 10 15 2 5 - X 5 ---- X 5 X 3 ---- X 3 = - =

  9. Review: to subtract fractions • If the fractions are not like fractions, convert them to equivalent like fractions • If you have no fraction, or too little of a fraction to subtract from, regroup one whole into the desired number of pieces (the denominator) and add them to the numerator • Subtract the numerators from each other in order and place the difference over the original denominator • Reduce the resulting fraction to lowest terms • Change improper fractions to mixed numbers

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