Learning To Subtract Well: A Subtraction Guide for Struggling Students

How to Subtract Well

Visualize the Operation

If you're having trouble with subtraction problems involving single-digit numbers, like 9 - 4, it may help you to visualize the process using objects. Keep in mind that the first number in the subtraction problem (9 - 4) always represents the amount of objects you're starting with. The second number (9 - 4) is the amount of objects that you're taking away. For 9 - 4, you begin with nine objects and take away four of them. The number remaining, five, is the answer (9 - 4 = 5).

Check Your Answer

When you're subtracting, you should be able to add your answer to the second number in the subtraction problem to get the first number. For example, imagine that you think 4 - 3 = 1. You could check your work by adding one and three. Since 1 + 3 = 4, your answer is correct.

Be Neat

One very simple way to subtract accurately when you're working with multi-digit numbers is to make sure that you're writing your problems neatly, which means the numbers should be lined up. If you have trouble keeping your calculations organized, try working on graph paper and putting one digit in each square. Some students also find it helpful to use a ruler to keep track of which digits they should be subtracting.

Understand Place Values

If you have trouble remembering how to subtract multi-digit numbers, it can be helpful to review place values. For instance, imagine that you're subtracting 119 from 321. Using the standard process, your first step would be to subtract nine from one, but you can't do that because nine is greater than one. It's common for students to get stuck on this step.

Each place in a number has a value equal to ten times that of the place on its right. For instance, 100 is ten times greater than ten, which is ten times greater than one. As a result, you can add ten to the ones place and subtract it from the tens place. In this problem, you can add ten to the digit in the ones place (one) to get 11 (1 + 10 = 11). The number 11 is large enough that you can subtract nine from it (11 - 9 = 2).

Since you added ten to the ones place, you must subtract a ten from the tens place. For this problem, there's a two in the tens place, so you'll need to change that to a one. Now, you can solve the remainder of the problem using the normal method (321 - 119 = 202).