Dan, the mechanic has 70 cars to fix this week. He wants to get 18 done today. How many will he have left after today?
This is a subtraction problem because we want to know how many cars Dan will have left after he completes some of them today. We take the total number of cars to fix and subtract the number that he plans to do today.
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.