N"> Amby's Math Resources - Procedure for Subtracting Fractions

# Working with Fractions, Step-by-Step

SUBTRACTING FRACTIONS

1.   WRITE THE NUMBERS VERTICALLY

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2.   DO YOU HAVE A COMMON DENOMINATOR?
(same bottom number = same size pieces)
NO:   Continue below...

Change to equivalent fractions with a common denominator:
• Find a number divisible by BOTH denominators (such as the LCM: Least Common Multiple).
• Multiply both the numerator AND denominator of one fraction by the SAME NUMBER to get an equivalent fraction with the common denominator.
• Repeat with the other fraction.

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3.   DO YOU NEED TO BORROW?

YES:   Continue below...

Borrow from the whole number:
• Mark how many whole ones remain after removing one of them.
• Add the number of pieces in one whole (the denominator) to the number of pieces you already have (the numerator) to find the total number of pieces from which you'll subtract.

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4.   DO the Subtraction:
• Subtract the numerators:   top minus bottom
(to find the remaining number of pieces).
Keep that denominator.
• Subtract the whole numbers (if any):   top minus bottom.

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5.

IS THE FRACTION IN LOWEST TERMS?

NO:   Continue below...

Reduce the fraction:
• Divide both the numerator and the denominator by the same number.
• Repeat until the only common factor is one.

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