Multiplication and Division

Checking Your Work

Checking your work after you divide is a good habit to develop. Checking helps you know that your answer is correct. To check the answer to a division problem, you'll need to use multiplication.

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  Let's look at this problem: 54 / 6 = 9.

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  How do we know that 9 is the correct answer? We can check by multiplying.

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  Let's set up our multiplication problem. First, we'll write the quotient. That means we'll write 9.

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  Next, we'll multiply the number that we divided by, 6.

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  Time to multiply. 9 x 6 = 54.

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  If we divided correctly, the answer will match the larger number in the division problem.

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  They are both 54. We checked the problem, and it was correct!

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  Let's try checking another problem. This time, the quotient has a remainder: 20 / 3 = 6 r2.

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  Let's set up our multiplication problem. First write the quotient without the remainder. That's 6.

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  Then multiply the amount that the larger number was divided by, 3.

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  Now it's time to multiply. 6 x 3 = 18.

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  Let's check to see if our answer matches the larger number in the division problem — 18 and 20. No, they aren't equal.

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  That may be because we haven't included the remainder, 2.

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  Since the answer to the division problem has a remainder...

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  Since the answer to the division problem has a remainder... just multiplying should give you a number less than the original number.

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  We'll set up an addition problem to add the 2 to 18.

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  Now add 18 and 2.

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  18 + 2 is 20.

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  Finally, check to see if 20 matches the larger number in the division problem. It does!

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In the slideshow, we used multiplication to check our division. The answer to the multiplication problem should always be the same as the larger number in the division problem. If your two answers don't match, check to see if you added the remainder. If your answers are still different, you might have made a mistake the first time you were dividing. Try solving the problem again.

 Long Division with Decimals

In this lesson, you also learned how to solve division problems that have a decimal in the answer. Checking your work for this type of problem is similar to checking other division problems. You'll follow the same steps.

We'll try checking this problem: 57 / 5 = 11.4.

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  Let's set up our multiplication problem.

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  We'll write the decimal quotient, 11.4.

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  Next, we'll multiply the number that we divided by, 5.

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  Now it's time to multiply: 11.4 x 5.

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  Since the quotient had one digit to the right of the decimal point...

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  Since the quotient had one digit to the right of the decimal point... we write the answer with one digit to the right of the decimal point. 11.4 x 5 = 57.0.

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  Finally, we'll check to see if 57.0 matches the larger number in our division problem. They are the same. Our answer was correct.

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