Know how to differentiate between separation problems, comparison problems, and part-whole problems when doing addition and subtraction.
Separtation (take away) one quantity given and remove certain amount. ex. tom has 13 pencils, he gave 3 to Sue. How many does he have?
Comparison (finding the difference) start with two quantities. You want to know the difference between the two. Tom has 11 pencils, Sue has 8 pencils. How many more does Tom have?
Part-Whole (how many in set) you are given how many are in entire set and how many in one part of a set, you have to find out how many in remaining set. Tom has 11 toy cars, 3 are toyotas, how many are hondas?