Skip to content
Slices

Fraction words

Common denominator

A shared bottom number, so two fractions are written with the same-size parts. Adding and subtracting need one.

Halves and fourths are different-sized pieces, so 1/2 + 1/4 cannot be counted directly. Writing 1/2 as 2/4 gives a common denominator: 2/4 + 1/4 = 3/4.

Adding the denominators does not work: 1/2 + 1/4 is not 2/6, because 2/6 is even less than the 1/2 we started with.

One half and one fourth, laid end to end, make three fourths.

See also: Equivalent fractions

Try it in a slice

Slice 16

Adding Different Pieces

Is (one half) + (one fourth) equal to (two sixths)?

Why 1/2 + 1/4 is 3/4, not 2/6: make the pieces the same size before you count them. · About 3 minutes

Slice 17

Keep the Unit When Adding

Is (one fifth) + (two fifths) equal to (three tenths)?

Why 1/5 + 2/5 is 3/5, not 3/10: joining fifths gives more fifths, not smaller pieces. · About 3 minutes

Slice 18

Taking Pieces Away

Is (three fourths) − (one half) equal to (two halves)?

Why 3/4 − 1/2 is 1/4, not 2/2: take away an amount using same-size pieces. · About 3 minutes