First have students memorize the math subtraction facts. These are simple problems with a minuend (top number) of 18 or less and a subtrahend (bottom number) that is one less than the value of the minuend. The answer is called the difference. The highest number is 18 because that is the standard, or proficiency, in most states for teaching subtraction facts in the second grade.
Memorizing the subtraction math facts will make it easier to calculate more complex problems. When first learning the subtraction facts, you can use Unifix Cubes to count out the minuend and find the difference by taking away the number of cubes in the subtrahend (see Resources).
Calculate problems with more than two numbers without regrouping. This is the easiest method for solving a math subtraction problem. In problems where each digit in the minuend is larger or the same as the digit below it in the subtrahend, you subtract the numbers just as you would in section 1.
Regrouping is a method of finding differences when the minuends are less than the subtrahend. For example, if any digit in the minuend is less than the number in the subtrahend, you have to regroup first by crossing out the digit in the next place over and subtract one from it and write that number on top of the digit in the tens place. Next, write the "1" in front of the number in the minuend in the ones place. Last, find the difference. In second grade, the numbers in problems are contain only three digits.
Check the problem by adding the digit in the difference to that in the subtrahend. If the number doesn't match the minuend value (including the regrouped digit mentioned in Section 3), then the problem is wrong and needs to be redone.