Checking Subtraction with Addition

1 of 8

What is the 'inverse operation' of subtraction?

Addition is the inverse, or opposite, of subtraction. They undo each other.

How can you use addition to check if your subtraction answer is correct?

Add your answer (the difference) to the number you subtracted (the subtrahend). The result should equal the number you started with (the minuend).

The subtraction problem is \(A - B = C\). What is the addition problem you would use to check it?

You would check if \(C + B = A\).

Let's check the problem \(85 - 20 = 65\). What addition sentence confirms this is correct?

\(65 + 20 = 85\). Since this is true, the original subtraction is correct.

You solved \(452 - 125 = 327\). How do you check your work?

Calculate \(327 + 125\). The sum is \(452\), so your answer is correct.

A student claims \(301 - 150 = 151\). Is this correct? Use addition to check.

Yes, it is correct. The check is \(151 + 150 = 301\).

Another student solved \(673 - 245 = 438\). Check this answer using addition. Is it correct?

No, it is incorrect. Checking with addition shows that \(438 + 245 = 683\), which is not the starting number of \(673\).

Why is it a good habit to check your subtraction problems?

It helps you catch and fix your own mistakes, especially with regrouping, and makes you more confident that your answer is right.