You may have read other posts about this long division shortcut at Math Mojo.
The main page to go to to learn the basics of the shortcut is:
Long Division Shortcut at Mathmojo.com
At that page, someone asked:
I have attempted this question using your method: 44872 / 79
Using your method I get the answer 569, when the answer is 568.
Please elaborate for me.
When I tried the example myself, I almost got 569 as well, but then I realized what the problem was. I think fellow who wrote, as well as I, fell prey to a very easy trap to fall into, and I’d like to address that now, because I imagine that other Math Mojo readers might benefit from it.
The best way to illustrate the problem, and the solution, is in a short video.
Please keep in mind that although I go through the division method in this video, I don’t teach the entire method. The video was made to simply address this one particular trap and how to avoid it. If you want to learn the method, go to:
Long Division Shortcut at Mathmojo.com
I do intend to have more thorough videos of the entire method up, after I finish the ones for addition and multiplication, which I’m working on now.
Warning: – After having to have about 9 takes to make that video, and then taking about a half-hour to process and upload it, I realized that at the end of the explanation I said something confusing. Damn!
I said that I would have looked at the second from the last multiple and picked it as the ninth. I even circled it. But it was the wrong one, obviously. I should have circled the eighth (the 632), and said “I would have looked and seen that the 632 was the third from the last multiple, making it the eighth, and written an 8 instead of a 9.” If you watch the video, you’ll see what I mean.
The vid was simply done to be able to respond to a reader’s legitimate question. I really will work on some more thorough ones eventually. I promise!
Click on the video below to learn how to avoid the “trap.”
Hi Professor Homunculus, Firstly allow me to applaud you on an exceptional contribution to Mathematics
and in my opinion the Human race, why are we all not having fun with Math. I
blame the poor UK curriculum. As the person whom raised this question to you, only late last on a Friday, I am touched that an answer came so soon and on the weekend! Your website is now top of my favorites list! Thank you very much and again well done.
Dear Professor Homunculus,
I have attempted this question using your method: 3650/242
and keep getting confused with the zero after the decimal place.
The answer is 15.08264 but using your method I get 15.8264
I am confused as to how I should know that at zero should be there.
Kind Regards
Claire
Professor Homunculus sez:
Claire,
That’s a good question. I tried it myself, and think I found the problem. At onw point, you endu up having to subtract 1210 from 1230, correct?
At that point, you get 20. Then you bring down a zero, making it 200. There, you have to ask yourself, “How many times does 242 go into that 200?” And the answer to that, of course, is zero.
I think you may have forgotten to write that zero as part of the quotient. It would go in the tenths position.
Then, after that, you would bring down another zero to make it 2000, and 242 would go into that 8 times, so the 8 would go in the hundredths position.
Each time you bring a digit down, you have to write something in quotient.
Do you see how that could be? Does that make sense to you?
I hope that clears it up.
To really make sure you understand the method, learn the details at Long Division at MathMojo.com
All the best,
Professor Homunculus
My 5th grader, who loves math, learned how to do the hangman form of long division last year, but has forgotten and has gotten rusty. i was not taught this form, and think it follows this key, but could you explain how to help teach a 10 year old this format?
Professor Homunculus sez:
Kate, I’m sorry to say that I don’t know or teach the hangman method.
Best of luck,
Brian
Hi professor Homonculus,
This is such an amazing trick/method to approaching long division. I am currently tutoring a girl and she has trouble with long division. While I was searching for tricks, I stumbled upon your brilliant method, and I have tried this problem, 79 into 44872 and have gotten 568. But I think I would mess up if not careful with the multiplication part of the method (multiplying by ones) because it’s one of the most essential steps. I never learned this while I was in grade school but thank you for sharing & teaching your knowledge with us.
Best,
Sadia
good
very useful method
Thanks a lot