Writing down that last math answer is a relief, but don't hand in that test or assignment just yet. Checking answers is a skill that improves your proficiency in math class. Use a variety of math checks to test the accuracy of your answers.
Ask yourself if your answer makes sense before you move on to another checking method. Read the question again, focusing on the operation and numbers involved. If you're solving a five-digit subtraction problem and your answer is larger than both of the original numbers, your logic check should tell you the answer is incorrect. Another way to do a general check is by estimating. If you're subtracting 2,345 from 5,421, for example, round the numbers off and see if your answer is close.
