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.
Check your answer with the opposite function. For a division problem, multiply your answer with the divisor, which should equal the dividend. For a multiplication problem, divide your answer by one of the two original numbers. The answer should be the other number. The same idea works for addition and subtraction. When solving an equation for a variable, plug your answer into the original equation. If your answer is x = 21, plug 21 into the equation x + 9 = 30 to verify the results.
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Try Another Way
It seems repetitive, but solving the problem again is an effective way to check answers. The answers should be the same both times you solve it. If not, look back through your work to find errors. Try a different method the second time when possible. Draw pictures to add two fractions the second time, for example. If you use a calculator for part of the problem, punch in the numbers again to ensure you didn't hit the wrong number the first time.