Intereting Posts

The Sorgenfrey line is hereditarily Lindelöf
Equivalence of weak forms of Hilbert's Nullstellensatz
Almost sure convergence of random variables
Probability distribution of sign changes in Brownian motion
recurrence relations for proportional division
Can a set be neither open nor closed?
Number of roots of a polynomial over a finite field
An integral that might be related to the modified Bessel function of second kind
Is it true that $|a^{\alpha} – b^{\alpha}| \leq |a-b|^{\alpha}$?
How many ways to merge N companies into one big company: Bell or Catalan?
Finding Eccentricity from the rotating ellipse formula
Why modern mathematics prefer $\sigma$-algebra to $\sigma$-ring in measure theory?
Best Strategy for a die game
Curves triangular numbers.
Are these 2 graphs isomorphic?

This is my first post. I hope it’s acceptable.

*EDIT* Since there are people to whom such notation is foreign, I will point out that the problem represents KRRAEE / KMS, where PEI is the quotient and KH is the remainder. KHHR represents P times KMS and ALH is KRRA minus KHHR; the E is “brought down” per division algorithm. The next two hunks are defined similarly.)

Because I want math students to become problem solvers in a manner than does not rely heavily on the “template-based” problem solutions that permeate math education at the middle-grade level, I would be interested in seeing written, easily-followed, mathematically- and logically-valid derivations of the solution to such division puzzles as the one below, such presentation being one that a reasonably competent “Algebra I” student could both follow and produce. (Maybe I just have a bad case of OCD, but I *daily* find joy in solving these puzzles, taking care to produce a presentation that just such a student could both follow and produce. Part of the joy stems from the belief that a summer project devoted to such problems could greatly enhance students’ problem-solving abilities.)

- How do you explain the concept of logarithm to a five year old?
- University topics appropriate for high-school contest preparation
- What is the meaning of the third derivative of a function at a point
- Mathematics - The big picture
- Is there a domain “larger” than (i.e., a supserset of) the complex number domain?
- Self-teaching myself math from pre-calc and beyond.

Spoiler alert: Answer follows. But since the requirement is that the solution be an actual *derivation*, go ahead and look. It’s hard enough without it.

Having given this a lot of thought, I think you might find the tableau below useful in organizing thoughts. It amounts to each non-vanishing “subtraction column” with blanks on either side of possible loaning and borrowing.

Before I post a solution I’ve arrived at, here is an outline that guides solution, whether writing it or following it.

The 3-deep-dashes symbol can be read “is congruent to (modulo 10)” [i.e, it says that the units digit of the multiplication on its left-hand side is found on its right-hand side.]

I find it hard to believe that, with long division’s future uncertain, this problem type will be easily swallowed; but the inherent mathematics and logic may turn the tide of opinion.

This is a particularly-easy problem of its type, chosen mainly because modular arithmetic, accessible to the target student audience, makes solution easier.

- What are the technical reasons that we must define vectors as “arrows” and carefully distinguish them from a point?
- How do I explain 2 to the power of zero equals 1 to a child
- New Elementary Function?
- Primary/Elementary Pedagogy: What is the rationale for the absent '+' in mixed fractions?
- What's the deal with integration?
- Why do units (from physics) behave like numbers?
- Is “A and B imply C” equivalent to “For all A such that B, C”?
- Is it to the students' advantage to learn the language of infinitesimals?
- How can I introduce complex numbers to precalculus students?
- Let $k \geq 3$; prove $2^k$ can be written as $(2m+1)^2+7(2n+1)^2$

It’s not hard to write out a solution in more readable form. Here’s a sketch, giving the key steps.

The little $HHL$ column shows that $L$ is either $0$ or $9$. Suppose that $L=9$. The $RHL$ column then shows that $R=H-1$. However, this means that $KRRA<KHHR$, which is impossible, so $L=0$, and $R=H+1$. From the $RHA$ column we see that $A=1$, and it follows from the $ARH$ column and the fact that $R=H+1$ that $H=5$ and $R=6$. We now have this:

```
PEI
KMS)K661EE
K556
----
105E
M5K
----
K01E
1PMM
----
K5
```

It’s clear from the last subtraction that $K=2$:

```
PEI
2MS)2661EE
2556
----
105E
M52
----
201E
1PMM
----
25
```

The middle subtraction shows that $E=1+2=3$:

```
P3I
2MS)266133
2556
----
1053
M52
----
2013
1PMM
----
25
```

The last subtraction now shows that $M=8$ and hence that $P=9$, and $9\cdot 28S=2556$ shows that $S=4$. Finally, we must have $284\cdot I=1988$, so $I=7$:

```
937
284)266133
2556
----
1053
852
----
2013
1988
----
25
```

Here’s the solution I arrived at one day recently. It’s in a format that I found, after much experimentation, to be one that MAYBE the target audience could both follow and use as a guide to writing their own solutions.

If the requirement were to write a truly-mathematical-looking derivation (ordered, with many words, from first equation down the page to last), NOBODY (including ME!) would be interested.

I truly believe that students at ANY level would become better problem solvers if given these (drum roll) PUZZLES–math FUN; math at its best? At least for young’uns. (And me!)

The use of color and the a), b), … guide could make this not only easier but even MORE fun–AND ACCESSIBLE.

Here’s another problem, significantly harder than the previous, but still accessible to target audience. The statement of the problem (i.e., northwest corner only) comes from a PennyDell puzzle magazine:

- $X^n + X + 1$ reducible in $\mathbb{F}_2$
- Is every connected metric space with at least two points uncountable?
- Is it always true that $(A_1 \cup A_2) \times (B_1 \cup B_2)=(A_1\times B_1) \cup (A_2 \times B_2)$
- Alternative proof that $(a^2+b^2)/(ab+1)$ is a square when it's an integer
- Using permutation matrix to get LU-Factorization with $A=UL$
- Can there be $N$ such that $P \equiv a \mod n$ a prime $\Rightarrow P+N$ also prime?
- Proof of the summation $n!=\sum_{k=0}^n \binom{n}{k}(n-k+1)^n(-1)^k$?
- Doubt about proof of factorization $f=pi$, where $i$ is acyclic cofibration and $p$ is fibration
- General method of integration when poles on contour
- Derivatives of the Struve functions $H_\nu(x)$, $L_\nu(x)$ and other related functions w.r.t. their index $\nu$
- Exponential curve fit
- The Langlands program for beginners
- The smallest 8 cubes to cover a regular tetrahedron
- rational angles with sines expressible with radicals
- If $f'(x) = 0$ for all $x \in \mathbb{Q}$, is $f$ constant?