Archive for the ‘Uncategorized’ Category

Summer Jobs Puzzle

April 9, 2009

oregonsummer2008I’m in the mood for a puzzle.  There are about a million on the web, but I liked this one from  Puzzlers Paradise because it talked about summer and because there was a cool grid that you can fill online here.  [You click once in a square to X it out, twice to put in the Yeah-I-got-it! circle, and three times thrice to clear it.].  The same site has a whole bunch of these, and a lot more puzzles on their main page.

This summer, five friends each found a different job to earn money. As it happened, they all started their new jobs in the same week; each on a different day and each earning a different amount. Determine the type of job each got, the day of the week each started working, each friend’s mode of transportation to their new job, and how much per hour each friend was earning.

1. Chris didn’t have a newspaper route but he did use the bus. The boy who mowed lawns took the train to work.

2. The boy who used a bicycle started working on Friday. Joe didn’t get a job as a painter.

3. The five friends are represented, in no particular order, by the following: the boy who made $6.00 per hour, the boy who started work on Thursday, the boy who used a car to get to work, Chris, and the boy who mowed lawns.

4. Peter started work the day before the boy who worked as a cashier but two days after the boy who made $7.00 per hour. The boy who worked as a cashier made $0.50 per hour more than Greg made.

5. The boy who started work on Tuesday made $6.25 per hour. Rob didn’t start work on Monday. Peter made more per hour than the painter but less than the boy who used a car.

6. Rob walked to work. The person who started on Wednesday didn’t make $6.50 per hour. The golf caddy used a car to get to work.

Good Luck!

The photo of the beach has nothing to do with summer jobs, but it was taken during the summer [by TwoPi, in Oregon].


Tax Math: Mesopotamia Stye

April 6, 2009

orientmitja2300acWe’ve talked about Aztec Taxes and Inca Taxes; what about taxes in Mespotamia?

There are many many tablets that can attest to the fact that they had them.  According to Dr. Tonia Sharlach at the University of Pennsylvania, lots and lots of things were taxed year round [Here’s a whole article about the salt tax!], with payment of objects instead of money.  This apparently led to a lot of smuggling, and Dr. Sharlach’s article quotes a letter from about 3900 years ago written by an office to an employee:

Irra’s son sent smuggled goods to Pushuken but his smuggled goods were intercepted. The Palace then threw Pushuken in jail! The guards are strong…please don’t smuggle anything else!

Apparently one of the worst taxes was the labor tax (sometimes called the “burden”).   While it sometimes feels like a certain amount of my job amounts to a labor tax, it’s admittedly quite a bit nicer than being somewhere else to work for a few months.

Upcoming…why is tax day April 15 anyway?

The map was posted under GNU-FDL by Nareklm.

Math Teachers at Play #4

April 4, 2009

balloonsIt’s been two weeks since the last Mathy carnival (oh Carnival of Mathematics, where aaaaaaarrrrrrrrrreeeeeeee you?), and on this snowy (seriously) April day nothing could be better than a nice long list of great blog posts.  And that’s exactly what there is at  Math Teachers at Play #4!    It’s being hosted over at Homeschool Bytes, a blog that shares a whole bunch of resources for homeschooling.  (Although they’re not limited to homeschooling, of course.  Our older kiddo is learning multiplication, and Timez Attack looks like a great way to  help him get the number facts at his fingertips.)

But back to the Carnival.  The carnival divided into different steps/levels, from counting money to the SATs [both the modern version and some questions that could have occurred if there were SATs in 1557], so there’s something for everyone.  Time to play!

The Abel Prize in rhyme

March 29, 2009

gromovThere once was a math guy from Russia
Which is just to the east of East Prussia.
He proved many a theorem.
Geometers revere him.
The Abel Committee did gusha.

They said to Mikhail Gromov,
(Whose sweater in this picture looks mauve)
“You are so creative!
A mathematical native!
You’re analysis’s own Brett Favre!”*

His work (expanding thresholds
Of n-dimensional manifolds
And related measure)
Gave people such pleasure
That this year’s Abel Prize he holds.

* No doubt they were referring to Brett’s heyday in the 90s, and not to last season.

For a more interesting but less poetic summary of his life and work, check out the official summary.

The Creative Commons picture of Mikhail Gromov was taken in 2007 by Gert-Martin Greuel.

In Good Company

March 23, 2009

beach_smileWe were thrilled to learn that we were mentioned in an article about math blogs that Jenni and Jon Ingram wrote for the March 2009 issue of Mathematics Teaching, a journal of The Association of Teachers of Mathematics in the UK.  Most of the articles (like the evocatively named “It would be 19 if 10 was an odd number” or “Puppets Count”) are only available to members, but a few, including theirs, are open to all.

They also wrote about dy/dan, Let’s Play Math!, and MathNotations,  with descriptions both of the blogs and of some samples posts for each.

Thanks for putting us in such good company!

The Beach Photo was taken by Richard Marris during the Kioloa Flickrmeet, Kiola, New South Wales, Australia [creative commons license].


March 17, 2009

pluto_hubble1What is a planet?

The current definition, from Resolution B5 of the International Astronomical Union, is that

A planet is a celestial body that
(a) is in orbit around the Sun,
(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and
(c) has cleared the neighbourhood around its orbit.

Pluto hasn’t cleared its orbit, so it’s not a planet.  There’s actually some controversy about this (and as usual, we turn to Wikipedia to learn all about it), but essentially that’s how things stand.  Pluto can at least rest assured that it’s not the first planet to be demoted.

But a lot of people don’t like that Pluto isn’t a planet, and last month the Illinois State Senate adopted a resolution that declared March 13, 2009 as “Pluto Day” and also included the line:

that as Pluto passes overhead through Illinois’ night skies, that it be reestablished with full planetary status

You can read the formal resultion here; it’s a short read, thought it packs no fewer than 10 “Whereas”s into just 1½ pages.   Here’s what is bothering me:  the bill’s sponsor, Senator Gary Dahl, apparently said:

I don’t think we are changing the status of the planet. We’re simply asking that March 13 be declared Pluto Day and that, for the day, Pluto is a planet.

But, if you add Pluto, aren’t you actually changing the definition of Planet?  If not in broad terms, at least by adding “and Pluto”? I get the distinct impression that he doesn’t understand what a definition is.  It reminds me of how our math majors often struggle with definitions when they’re first learning how to write proofs:  starting from the definition of an even integer (twice an integer), it’s initially hard for them to prove that if n is even, then so is n+2.

And yes, I might be making too much of this.  I don’t want to begrudge Pluto its special day.  But still.

One Two Three

March 7, 2009

twoTime for some math problems!  I was initially going to share two interesting problems featuring the number 2, but then it turned out I’d done one of them wrong and the answer wasn’t 2 at all.  But then I turned to the digits 1 and 3, and they saved the day.  Hooray!

Problem #1 is about amicable pairs.  These are numbers each of whose proper divisors add to the other number.  For example, 220 and 284 are amicable, because the proper divisors of 220 (1,2,4,5,10,11,20,22,44,55,110) add to 284, and the proper divisors of 284 (1,2,4,71,142) add to 220.  And that’s the example you’re going to find if you do any sort of search for amicable pairs, because the next pair is 1184 and 1210.  Not that they are so uncommon (there are about 12 million known pairs), but they do tend to be pretty big.

So anyway, take any amicable pair.  Start with the first number, add the reciprocals of all of its divisors, and then take the reciprocal of the sum [i.e. (1/1+1/2+1/4+…+1/220)-1].  Do the same thing to the other number [i.e. (1/1+1/2+1/4+…+1/284)-1].  Then add those two numbers together, and you’ll get 1.

Pretty neat, huh?  And the proof isn’t too bad (it involves putting each sum over a common denominator and falls into place from that, where “falls into place” can mean anything from you see it right away to six hours of staring).

Problem #2:  I learned of this problem via Ted’s comment here.  (Thanks Ted!)   He linked to Ron Knott’s site, which has all sorts of stuff about generating Pythagorean Triples, including this algorithm:

  • Start with two fractions that multiply to 2:  for example, 3/4 and 16/6.
  • Add 2 to each number:  11/4 and 28/6
  • Put the numbers over a common denominator:  33/12 and 56/12
  • The numerators will be the first two numbers of a Pythagorean Triple:  332+562=652

Isn’t that cool??  Furthermore, you’ll get primitive triples exactly when you start with reduced fractions (and use the least common denominator in the third step).

Problem #3 is about base 3.  Find all positive integers n such that neither n nor n2 have any 1s when written in Base 3.  And since I told you the answers to the first two problems and just left off the proofs, I think I’ll leave off the answer to this and let you see if you can find them all.    Happy Problem Solving!

Two great sites

March 6, 2009

Here’s what I saw when I checked out xkcd this morning:

(I’ll admit, it took me a moment to get, after which I decided it was one of my favorite strips.)

So that was one great way to start the day.  Then I found that Denise had posted Math Teachers at Play #2.  And it has, like, a million fantastic posts, plus the picture are really cute.  So that was another great way to start the day.

Plus it’s Friday.  It doesn’t get much better than that.

Square Root Day!

March 3, 2009

carrotsI was driving into work today, and when I turned on my radio I heard that it was Square Root Day.  Except I missed the part where they were explaining what it is, and all I heard was that it won’t happen again for a while, and I thought to myself, “Huh?  But isn’t EVERY day a square root day, since 3 is the square root of 9, and tomorrow, the 4th, will be the square root of 16?”  And I was completely confused.

Then just a few minutes ago, my friend Cheryl popped into my office and said, “HAPPY SQUARE ROOT DAY!”  And she was able to explain this holiday:  it’s because it’s 3-3-09, and 3 is the square root of 09.  Then the light shown shone down and angles sang* and it all made sense.  And the radio was right about the rarity — the next one isn’t until 4-4-16.

And as soon as Cheryl left, my student Adele popped into my office and apologized for overhearing our conversion (nice of her, but unnecessary — my office is right off of the Math Center and I listen to student conversations all the time).  Anyway, Adele passed along that she also had heard about Square Root Day!  It turns out that it’s all over the internet.  Apparently you’re supposed to eat root vegetables cut into squares.  This might explain why it’s not as celebrated a holiday as Pi(e) Day.  So without further ado,

Happy Square Root Day!

Just so I’m not behind on another holiday, Thursday and Saturday are Odd Days, since 3-5-9 and 3-7-9 are odd numbers in increasing order.  Celebrate away!

*I started to write “angels” and misspelled it, but decided that angles singing was more appropriate.

There’s a new Carnival in Town!

February 20, 2009

notting_hill_carnival_crowd_-_august_2006Posted today is the inaugural edition of a new Carnival: Math Teacher at Play. This carnival is the brainchild of Denise at Let’s Play Math, who wanted a gathering that focused on posts that were appropriate to teaching elementary school through high school mathematics.  Because this is complementary to the Carnival of Mathematics, it will appear every other Friday, when the Carnival of Mathematics is not in session.  This means that we’ll have Math Carnivals every Friday — hooray!

The Carnival will initially be hosted at Let’s Play Math, but Denise welcomes other hosts. This first edition has 20 entries (wow!) gathered by Denise, and I look forward to reading them all!

The photo above is from Diliff (posted under GNU-FDL) and it actually shows a crowd at a carnival in Nottingham, but I’m sure that they would have wanted even more to be at this carnival.

Unzipping the Klein Bottle

February 10, 2009

ACME Klein Bottle The Klein Bottle.  I remember first learning about it,  and it was, well, hard to visualize.  (“Self intersecting?  The outside and inside all the same?  Hanging out in four-dimensional space?  Ummm, okay.”)  Then I discovered ACME Klein bottles, and they made my life happy because I could sort of understand what a Klein bottle was, and because their web page is fun to read.  Plus, they sell Klein Steins:

klein-stein-small(Godzilla finished his beverage before I got a chance to photograph it.)

One feature of a Klein bottle is that it can be made from two Möbius strips.   Another thing that was hard for me to picture (though again Clifford Stoll at ACME comes to the rescue), but I just ran across this video of a Klein bottle that had been made by zipping together two Möbius strips, and I thought it was so neat that I wanted to share it.  I might just have to figure out how to work the sewing machine just so I can make one.

(And really, I’d just intended this post to end here, but then I found the following clip and couldn’t resist adding it!)

ACME Klein Bottle photo by Lethe, published under GNU Free Documentation License.

Carnival #49 this Friday!

February 9, 2009

clown at the carnivalWe’ll be hosting the Carnival of Mathematics #49 on Friday the 13th, so send in your submissions by midnight Thursday (which really means early in the morning Friday)!  You can post them in the comments here, or use the official form (which seems to be working fine — I’ve been getting submissions that way), or send them by email to hlewis5 followed by the @ sign followed by

Ode to Eday

February 7, 2009

klein_e3Today is e-day — the day that millions come together worldwide in praise and glory of the number e, which is approximately 2.718…

But this is not the only e-day.  Indeed, there are many others that appear to have nothing at all to do with the number.

  • In Paducah, Kentucky E-day falls on February 21 and refers to Engineers Day.  They have an egg drop contest, tape people to walls, and create edible cars.
  • January 1, 2002 was Euro Day, when a whole bunch of countries simultaneous adopted the Euro.  Right now 1 Euro is worth 1.2944 US dollars according to Google.   Speaking of Google, did you know that their Zurich office has twirly slides, fireman poles, and meeting rooms in the shape of  igloos?
  • eDay in New Zealand is the day that people can get rid of their e-waste (which to me sounds like spam, but means old computers).  Old electronics get sent out to recycling places instead of the landfill.
  • And then there’s my favorite:  the island of Eday in northern Scotland, one of the Orkney islands.
    eday131 people live there (as of last summer), and the main exports have been peat and limestone (and pirates!  Or at least one pirate:  John Gow).  They have a new Heritage and Visitor Centre, and enough B&Bs for a local tourists.  There is however, no evidence of a “Spend e-day on Eday!” marketing  campaign — they might want to try that.*

*Using the 2 July version of e-Day, presumably. Though today it’s a balmy 34°F up on the isle, so perhaps it could be a biannual tradition.

The fancy e was created by Acf and is available under the GNU Free Documentation License.

Dimension Confusion

February 2, 2009

tv_antikSo how about that Super Bowl?   Having analyzed the game here yesterday (OK, not the actual game, but potential scores) it’s time to reflect on the commercials.  The sense seems to be that the commercials were…OK.  Some pretty funny ones, but not one of the absolute best years ever for commercials.

And from a math perspective, one commercial stood out.

Although come to think of it, the 1D version of Chuck might be really entertaining!  The ultimate stick figures.

What’s the pattern?

January 25, 2009

Question Mark1, 11, 21, 1211, 111221, 312211, 13112221, …

This sequence was the favorite pattern of my former department chair, Nelson Rich.  I thought he invented it, but a quick search on the internet reveals that it’s pretty easy to find if you search for the first few terms.

But don’t do that! It’s a sneaky one, but fun to try and figure out.

If you want a hint, click here.