FractionsTo 12
Mixed numbers to improper fractions worksheets
Turning 3 1/4 into 13/4 is the conversion every fraction calculation needs sooner or later. These free printable worksheets ask for the improper form, with denominators up to twelve.
If they get stuck

The answer key prints on a separate page.
What's on this sheet
Three wholes at four quarters each is twelve quarters, and one more makes thirteen. That sentence is the whole method, and it is better than the rule it produces — a child who has said it once can rebuild multiply-then-add whenever they need it, while a child who only learned the rule has nothing to fall back on when they misremember which way around it goes.
Why this sheet works
The direction matters because multiplication and division are the two operations that cannot be done on a mixed number as it stands. 2 1/2 × 3 has to become 5/2 × 3 before anything sensible happens, which is why this conversion is taught just before those.
How this one works
One question from a sheet like this one, worked a step at a time — with a sentence saying what just happened and why.
Mixed numbers to improper fractions, step by step