Teaching Subtraction

I wanted to make subtraction easier to understand for our nine year old daughter. The commonly used method has too many conditionals (do something different based on this particular case) and so I devised a method of teaching subtraction that uses the same steps for each digit regardless of the values in this column or previous columns. Once your child has mastered the sequence of steps for deducing one digit of the answer he/she can perform subtraction of numbers of any length. I am not the first to think of this method for teaching subtraction (For someone else's explanation see link to "Arabic Numerals - subtraction" at the bottom of this page), but I for one haven't seen it taught to children in any school.

Start at the right column of the two numbers. If the rightmost digit in the minuend (top number) is greater than or equal to the rightmost digit in the subtrahend (number you are subtracting from the top number) then just write the difference in the rightmost digit of the difference (the answer). However, if the minuend digit is less than the subtrahend digit then first add ten to the minuend digit and add one to the subtrahend digit in the column just to the left of the column on which you're currently working. After adding the 10 and the 1, do the subtraction for this column and then move left to the next digit. That's it! Just keep on moving left, applying the same rule until the subtraction is finished.

The reason teaching subtraction using this method makes it easier for young kids to understand is that the commonly taught "borrow" method (borrow "1" from the digit to the left) becomes more complicated if the digit to the left is a "0". Young children don't do well with negative one, and the above described method does away with that problem.

Please visit the latest version of this article on our web-site which includes a diagram comparing the two methods: Teaching Subtraction.

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Arabic Numerals subtraction