Long Division Shortcut (Part 3)

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We’ve been talking about using factors to make long-division problems easier, sometimes being able to turn them into a manageable sequence of short-division problems, in which no paper and pencil (and certainly no calculators!) are needed.

Want to try another one? How about

962/52 ?

Well, they’re both even, so that’s going to be a piece of cake to start. Divide both by 2 and turn the problem into:

481/26

Can you factor them further? You can tell that 2 won’t be a factor. And a quick look at 26 tells you that 3,4,5,6,7,8,9 and 10 won’t factor into it. It’s only factor, other than itself and 1 is 13. When you factor 13 into 21, you get 2.

Now all you have to do is test if 481 is divisible by 13. If you know the trick to test for divisibility by 13, you could try that, but let’s just assume you don’t, and go ahead and divide it in our heads.

13 goes into 48 three times, with 9 left over. Carry the 9 to the front of the 1 in 481, and get 91. Divide that by 13, and whaddyaknow, it goes in exactly seven times. That gives us 37.

We have reduced the problem from

without much trouble, and no writing. I think you can handle 37/2 on your own from here.

Right, it’s 18, r. 1.

Remember, that’ the answer to 37/2. But if you want to check it as the answer to 962/52, you’re going to have to re-factor in the 13 and the 2 to the remainder. When you multiply the remainder (1) by the factors (2 and 13) you get 1 x 2 x 13, which is 26.

Checking 962/52 = 18, r. 26

962/52 = 18 r. 26

So the crunch to the problem is 0, remainder 26.

So the crunch to the answer is 0, remainder 26.

The crunch to the problem matches the crunch to the answer, so the answer is very probably right.

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