Talk:Long division

Netherlands example

My recent edit attempting to 'fix' the Netherlands notation was reverted: https://en.wikipedia.org/w/index.php?title=Long_division&oldid=prev&diff=885090732

The commit message for the revert said the original example was correct, and that my example had errors. That's quite possibly true, and if so it is an indication that this section needs more explanation.

In particular, the one thing that could really help would be to use the same example that is used elsewhere in the page (127 / 4) rather than a new example that has nothing to be compared against.

Can someone with appropriate knowledge update the expression to demonstrate 127 / 4. If the updated example does not obviously relate to the earlier examples then some additional explanation of the differences would also be helpful.

Kind regards,

-- HappyDog (talk) 19:05, 9 March 2019 (UTC)

For information your example misaligned the columns, and then assumed that 30/4 = 6 r 6 when of course you can never have a remainder of 6 from a division by 4. I do accept your point about using a common example, the multiplicity of examples comes from the multiple editors. However I think that 127/4 is a very bad case to take. Most people would do this by mental arithmetic and if written down would normally use short division. Indeed, I suspect the reason you made a slip on the working is that you knew the answer before the working! I may try over the next few days to move to common examples, but using a slightly more realistic long division. Regards, Martin of Sheffield (talk) 21:27, 9 March 2019 (UTC)

To be honest, I just copied the examples from up the page, formatting them based on how I understood the Dutch method to be formatted, based on the previous example. However, it looks like I must have made a copy/paste error and kept the last few rows of the previous calculation. Oops! Instead of 24/60/60/0 it should have been 28/20/20/0. Sorry about that.

In terms of your point about 'realistic examples', actually I think there might be some benefit in keeping it as something that people can work out in their heads - this page is supposed to explain the concepts and techniques so keeping it simple is probably more understandable.

Either way, I'll let you tinker with it and update as appropriate. --HappyDog (talk) 23:42, 9 March 2019 (UTC)

Proof of existence and uniqueness of $\beta _{i}$ not clear

The proof in the article does not seem clear to me. It does not prove the fact that $\beta _{i}<b$. Also, why does it not use the Euclidean division?

Here is a proof:

$d_{i}$ can be divided by $m$, see Euclidean division. So there exist $q$ and $r$ such that $d_{i}=mq+r$ and $0\leq r<m$. If one shows that $q<b$, then we have found $\beta _{i}$ and $r_{i}$ as $\beta _{i}=q$ and $r_{i}=r$.

We proceed by induction. At $i=0$, $d_{i}$ is formed by the first $l+1$ digits of $n$, so it has $l+1$ digits, which is the total number of digits of $m$. Then, $q$ cannot be equal or larger than $b$, since, $qm$ would be a number with $l+2$ or more digits, and it would be $d_{i}<qm$. This contradicts $r\geq 0$. So, we must have $q<b$.

Now, assume $d_{i}=m\beta _{i}+r_{i}$ with $0\leq r_{i}<m$. Then, by definition, $d_{i+i}=br_{i}+\alpha _{i+1+l}$. That is, $d_{i+1}$ is $r_{i}$ shifted to the left with the $\alpha _{i+1+l}$ digit added to the new place to the right. Since, $r_{i}<m$, the number of digits of $r_{i}$ is less than or equal to those of $m$, that is $l+1$. The hardest case to check is when its digits are exactly $l+1$. Let's write down the digits of $r_{i}$, $d_{i+1}$ and $m$

$r_{i}=aa\ldots as\ldots$

$m=aa\ldots at\ldots$

$d_{i+1}=aa\ldots as\ldots \alpha _{i+1+l}$

where we assume that some initial digits of $r_{i}$ and $m$ may be the same, but surely at some point, some digit must differ and, in particular, $s<t$ since $r_{i}<m$. Notice that $d_{i+1}$ has l+2 digits.

If one multiplies $m$ by $b$, $m$ shifts to the left and the $t$ digit goes at the same position of the $s$ digit of $d_{i+1}$, since now both of them have l+2 digits and since $d_{i+1}$ is, in its initial part, equal to $r_{i}$. Thus, it follows that $bm>d_{i+1}$. So, chosing a number $b$ or greater, one cannot divide $d_{i+1}$ by m. Since we can (by the Euclidean division), the quotient must be $q<b$.

The other case where the number of digits of $r_{i}$ is less than those of $m$ is handled similarly to the $i=0$ case: multiplying by b would shift m and yield a too large number.

Alopumo (talk) 17:25, 20 September 2019 (UTC)

Wrong subscript in equation

Equation $d_{i}=br_{i-1}+\alpha _{i+l-1}$ should be $d_{i}=br_{i-1}+\alpha _{i+l}$ instead. In fact, if you see the expression of $r_{-1}$, the last $\alpha$ digit is $\alpha _{l-1}$, so the first to be added in $d_{0}$ is $\alpha _{i+l}=\alpha _{l}$, which is, rightly the successive one.

Alopumo (talk) 17:25, 20 September 2019 (UTC)

Two halves of Belgium

Under the section on conventions in Eurasia, the Belgian standard is said to be the French one:

    127|4    
   −124|31,75
      30
     −28
       20
      −20
        0

However, I do not recognise this form, yet I'm from Belgium. The notation I was taught, both in elementary school as well as in high school and then in university, is what the article assigns to Cyprus (and strangely, also France):

6	3	5	9	17
− 5	1			374
1	2	5
− 1	1	9
		6	9
	−	6	8
			1

My guess is that either of the following is the case: either Belgium was misplaced, or this has something to do with the Flemish/French division running through the central latitude of the country. I'm based in Flanders, and I do believe everyone here is taught the latter of the two notations. I'm not editing the article because I don't know which of my guesses is correct, but it might be worthwhile for others to chime in. MewTheEditor (talk) 19:56, 7 November 2020 (UTC)

Mixed mode long division

the given example mentions 15 inc left over which is 12+3 while the column top about inch mentions 9 further in the first cq miles column the multiplier is given 1760, but in the yardscolumn the multiplier VALUE is ommitted which is e for 22x3=66, just as in the feet column. there are MANY mistakes in this example!!! — Preceding unsigned comment added by 85.149.83.125 (talk) 14:46, 10 April 2023 (UTC)