Sam has a box of candy with 52 pieces of candy left. The box had 100 pieces of candy before. How many pieces of candy has Sam eaten from the box?
This is a subtraction problem because we want to know how many pieces of candy Sam has eaten. We take the total number of candy pieces which is 100 and then we subtract the number of candy pieces that are left in the box.
The keywords to look out for in a problem involving subtraction are: take away; how many more; how many less; how many left; greater; smaller.