Why the hell would you teach subtraction like that?


Our CEO, Maria, always tells me that I should not swear on the company blog. Today is trying my patience in complying with that policy because I think some of the ways math is taught are just unbelievably, inexplicably stupid.

Take the counting up method of teaching subtraction. Now, I think this makes perfect sense if you are doing math in your head and you have numbers that are close together. For example, if you are subtracting 945-939. You can easily count up from 939 to 945 and find your correct answer of six. This makes perfect sense to me.

Now I don’t know if you have looked at any of the material supposedly showing children how to use counting up to subtract two numbers but I have and I find it incredibly stupid. This is how you’re supposed to do if you are subtracting 962-481.

First, you count up to the nearest 10 so 9+481 = 490. Remember the nine.

Second you connect to the nearest 100, 490+10 = 500. Remember the 10.

Third, you count up to equal the hundred place, in other words, you add 400 to the 500 to get 900. Remember that 400.

Fourth, since you are at 900, you add the numbers after 900, in this case 62.

Fifth, you add all four of those numbers together, 9+10+400+62 = 481.

That is indeed the correct answer so I’m not arguing that the math doesn’t work but it seems an incredibly wasteful, useless way to subtract. The whole point of mental math is that you do it in your head. I don’t see anyone doing this method in her head. So, why don’t you just use a calculator?

The other reason that I hate this method is that it is the exact opposite of what I believe children need. They need lots of experience with numbers that makes sense. The reason that your parents and I learned this concept of “borrowing” from the tens place for the hundreds place is that it taught us that there was a relationship between the digits and the place value. It emphasized that if you went from 8+2 that was 10 and that was in the next place. If you went from 80+20 you got to 100 and that was in the place to the left of the tens place. I’m not sure what the hell this counting on method is supposed to do.

If the only point is to be able to do subtraction of larger numbers without a calculator I’m not sure what good that is. I am 59 years old, have a PhD and two masters degrees and I’m at the bank and I need to subtract 4877-1639 , I will use the calculator on my phone and I sure as hell won’t pull out a piece of paper and use the counting up method!

By the way, subtraction is covered briefly in the game Spirit Lake, before we get into multiplication and division. We do not use this method. Check it out and play on Mac or Windows.

Spirit Lake linked to buy game

Leave a comment

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.