Inside Lane

Long Division–the even longer way

Like a lot of parents, I am terrified of my child’s homework. Not only did I do enough of it as a child (or maybe not enough of it, if you look at my old report cards), I don’t know HOW to do his. Half of what he does is computer, or tablet based, and I am just excited when I can figure out how to dump a YouTube video into a blog entry from my phone (see below.)

We had a math meltdown the other night, when I tried to help Thor with long division. I took a glance at the way he was doing it, and was convinced he had completely misunderstood (or ignored) whatever it was he had been taught, and tried to gently tell him that his work was bassackwards. Those of you with children will know exactly how well that went.

Turns out, he was doing it correctly, and once I got the hang of his system, I liked it. Dare I say, I liked it better than the old way.

Below, I posted a video of my way to divide 4615 by 65, and his.

The main differences are that in my way, the divisor goes into the divisible from left to right. Can 65 go into 4? No. 46? No. 461? Yes. And that gives you the placement of the first number for your answer–across the top of your dividing hut.

You keep working your way across, until you can’t divide any further, or you have a repeating remainder.

Thor’s way, you consider the whole of the divisible, and ask yourself what-multiplied-by the divisor is less than that number. You can pick anything, from 1 to whatever number fits.

In this case, Thor just picked an 8 out of nowhere. He multiplied 65 by 8, then subtracted that number (520) from 4615. With 4095 left over, he decided to go for a bigger number, and picked 20 the next time. He repeated that three times, until he only had 195 left, and then had to pick 3.

He added 8+20+20+20+3 and came up with the same answer I did.

It doesn’t explain easily, evidenced by the tears shed last night, but it works, and it works well. I can wrap my brain around that pretty easily because it doesn’t require that I be able to multiply easily in my head. I can just pull numbers out of the air, all day long, then add them up.

I was actually surprised at how stress-relieving his way was. You can work your way into the correct answer without killing yourself multiplying all kinds of combinations to get to the single correct number you are looking to find.

Anyway, score one for Common Core. The kid can divide, and he can make change, so I guess he’ll be all right.


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