Integers, add and subtractWithin 20
Add or subtract the integers.
Integers add negative numbers to the mix, and the sign rules are the whole challenge. These free printable worksheets drill adding and subtracting positive and negative numbers, with the sign combinations mixed together.
If they get stuck

The answer key prints on a separate page.
Adding a negative is subtracting; subtracting a negative is adding. Stated as rules they blur together, so practice is the thing that makes them stick. Sheets mix the two operations across a chosen range so a child meets every sign combination rather than one at a time.
Integers are the doorway to algebra, where negatives appear on both sides of every equation.
One question from a sheet like this one, worked a step at a time — with a sentence saying what just happened and why.
Integer operations, step by step