_______ means opposite. _______ __________ undo each other. We use them to check our work.

An ________ has an equal sign. Both sides of the equals sign have the same value.

a letter or symbol that stands for an unknown number.

You can change the order of numbers when you add to make addition easier. You will still get the same sum.

the answer to a subtraction problem

You can change the grouping of numbers when you add to make addition easier. You will still get the same sum.

In subtraction, start from the smaller number and count on until you get to the larger number.

The sum of a number and ZERO is equal to that number.

the answer to an addition problem