Definition
Fraction subtraction
Fraction subtraction finds what remains or the difference between compatible fractional amounts.
What it means
First check that both fractions describe the same-sized whole or unit. Then make the pieces the same size, using equivalent fractions when needed. Subtract how many of those equal-sized pieces are removed.
Remember it
Same whole, same piece size, then take away.
Example
A bottle holds 7/10 litre and 3/10 litre is poured out. The same-size tenths can be subtracted: 7/10 − 3/10 = 4/10 = 2/5 litre.
Watch for
Subtracting fractions of different-sized wholes without naming a common unit does not give a meaningful single fraction.
Common mix-up
Do not subtract the denominators. Keep the part size and subtract the number of parts.
Exact meaning
Fraction subtraction removes one fractional quantity from another or finds their difference when both refer to compatible wholes or the same unit. The fractions must be expressed with compatible part sizes before their counts are subtracted.