## Monday, February 23, 2009

### Odds and 'Even' More Updates Week of 2-23-09

World Math Day '09
On March 4th, there will be the biggest online math contest on the planet! Registration and practice is now open for this event. Unite with students and schools from around the world to set a new world record! The Challenge - to correctly answer more than 182,445,169 questions in 48 hours.

- An Alternative Carnival of Math for PreK-12
Congratulations and Best Wishes to Denise at let's Play Math for this ambitious undertaking. Her inaugural edition is now up and running and I rate it a 10++++. She has links to nearly 20 math blogs and does justice to every one of them. Denise will need our support to keep this going.

Do any of you recall that I originally proposed a similar split in the 10th Edition of the Carnival of Math? It took Denise's courage and talent to make this a reality.

Dynamath - A New Student Math Blog
The author, currently a high school student and a former student of mine, goes by the moniker, Blabbermath. She introduced me to her blog a few days ago and I emailed her my comments and thoughts about her first few posts. She exemplifies everything I always looked for in that special student -- curiosity, insight, fearlessness in following her thought processes as far as they will take her and she is a darn good problem poser not to mention a talented writer. Try some of her challenges. I warn you - it can be addictive!

So who noticed the Amazing Decimal-Fraction Calculator in the sidebar? Surely you've always wondered about the pattern in the decimal representation of 1/9801? Now you can explore more decimal places than you ever thought possible:
1/9801 = 0.000102030405060708091011121314151617...
So when does this pattern start repeating? Go to the link in the sidebar to find out, then explore on your own...

1800-TEACHER.com Singapore's Education Network

Here's the invitation and terms from the authors of the site:
These worksheets are “school examination papers” contributed by parents and students over the years. The information contained herein is in the public domain. These worksheets are provided by 1800-TEACHER as a service to the community. You may download or print these worksheets for personal use only.

You need to register for free before you can download but it is worth it. For copyright reasons, I will not reproduce any questions here but I strongly urge you to look at the content and levels of difficulty of these assessments for the "primary" grades.

Pat's Blog
Pat Ballew has an excellent math blog and he and I often cross-reference each other. Pat expanded on the contest problem I posted the other day with a wonderful extension. This is a great question for your stronger 2nd year Algebra students. Building on each other's ideas is what Web 2.0 is all about! Thanks, Pat...

## Friday, February 20, 2009

### Updates and A Challenge Problem From Our First Contest

• There are some 'new' math blogs (in some cases, new to me!) that I wish to bring to your attention. One of these was just started by one of my former students who is still in high school. She made excellent contributions to MathNotations last year. I'll post a link shortly. Look for creative thinking, challenging problems and an engaging writing style!
• Look for the Math Problem of the Day in the right sidebar. This is a 'gadget' made available by Blogger. Nice problems which are accessible to advanced middle schoolers and secondary students. They change every day so try them and check the solution link which is provided.
• There's a wonderful fraction calculator out there on the Web to which I will post a link and publish an article in a few days. If you haven't seen it, it will blow your mind! Imagine seeing the decimal expansion of any rational number to any desired number of places (within limits) instantly and that's not all it does!
• Yes, Pi Day is coming so I will post links to previous articles I've published and other excellent resources out there.
• Some of you know there's an excellent free resource of Singapore Math assessments for primary grades and more. You can download these and use them for your students. they make wonderful Problems of the Day and discussion points for your next department meeting! I'll post a link in a few days. Wait till you see the level of thinking and the content in the Grade 3 assessment, for example.

The following was question 5 from our contest. I'll leave it up for you to try. Feel free to comment or solve. This question proved to be of moderate difficulty for the teams. One has to be very careful about adhering to all the conditions regarding points P, Q and V. Have fun with it!

Problem 5 (2 pt question)

The graphs of y = 2x+3 and y = -x2 + bx + c intersect in 2 distinct points P and Q, where P is on the y-axis. Let V denote the vertex of the graph of the parabola.

(a) Determine all values of b for which the points Q and V coincide.
(b) Determine all values of b for which Q and V are distinct and the slope of line QV equals 3.

## Tuesday, February 17, 2009

### Results of First Math Notations Contest!!

"It was such a pleasure for me to see students so excited about math. Great job, Dave!"
Maureen Capuzzi, Montville HS

"I thought you might be interested to know that the moms appreciated your contest enough to ask for another one---for next week!"
Denise, Decatur Area Homeschoolers

"we all had a few 'a ha!' moments, which I think is the best part of math..."
ecv at fhs

FIRST PLACE (11 out of 11 pts)

SECOND PLACE
MONTVILLE Twp HS, Montville, NJ

THIRD PLACE (Tie)
FAYETTEVILLE MANLIUS HS, Manlius, NY

FLORIDA MU ALPHA THETA TEAM, Tallahassee, Vero Beach, Fl

WYEDEAN HS, Chepstow, England

FOURTH PLACE (Tie)

DECATUR AREA HOMESCHOOLERS, Decatur, Il

WALLINGTON JR/SR HS, Wallington, NJ

FIFTH PLACE (Tie)

FORT VANCOUVER HS, Vancouver, WA

LAKE STEVENS HS, Lake Stevens, WA

TAHOMA HS, Maple Valley, WA

Congratulations to our other participating teams, some of whom consisted of middle schoolers. This contest proved very ambitious for students below grade 11 but I hope it was a valuable learning experience for all. In the future, I plan to have separate contests for middle and secondary schools. THE NEXT FREE CONTEST IS SCHEDULED FOR APRIL OR MAY - STAY TUNED!

I also plan on posting some of the contest problems over the next few days. This has been an interesting experience for me and I learned much from the comments of the advisors and students. Next time I will limit the time to 30-45 minutes for ease of scheduling! If you think you might be interested in our next contest, you can always email me early and let me know. (dmarain at gmail dot com).

## Thursday, February 12, 2009

### Friday the 13th Parts I, II and III in 2009: Feb, Mar and Nov. Is this unusual?

Update: See detailed info on Fri 13th at bottom. Also, several revisions have been made.

Update on Contest:

All teams' Answer Forms have been submitted and scored. The highest score was a perfect 11 out of 11. There were several other outstanding scores as well. More details to follow...

If you suffer from triskaidekaphobia, uh, well, maybe you can be Rip Van Winkle starting tonight, Thu Mar 12th, and wake up on August 14th next year. Next year will be much less scary with only one Friday the 13th!
Note: Triskaidekaphobia only refers to fear of the number 13. See the Wikipedia article for the very long word denoting fear of Friday the 13th!

Can this be a learning experience for our students?
Here are some questions to ask:

Feb 13th 2009 happens to fall on a Friday.

Q: What day of the week will it be 28 days later? Explain.
Ans: Friday
Explanation: The days of the week repeat every 7 days and 28 is a multiple of 7.

Q: What day of the month will it be 28 days after Feb 13th? Explain.
Ans: It will be the 13th of the next month, in this case, March.

Explanation--
BASIC RULE:
If today is the nth day of a given month and there are k days in this month, then k days from today will always be the nth day of the following month!
Why? Well, we can write k = (k-n) + n, which can be interpreted to mean that k days from today will be the nth day of the following month.

Ok, an example would help here:
Let's say today is the 5th day of some month and there are 31 days in that month. We can write 31 = (31-5) + 5 = 26 + 5. the "26" brings us to the end of the month and then we add 5 more days which brings us to the 5th of the next month. Make sense?

Putting this all together, 28 days from Friday Feb 13th will be Friday March 13th. The key was that 28 is BOTH the number of days in the month AND a multiple of 7!
That wasn't hard, but now for the tougher question:

Q: Why is there going to be a third Friday the 13th in 2009, namely Nov 13th?

Explanation:
Mar-31 Cum. Total = 31 (not div by 7)
Apr-30 Cum. Total = 61 (not div by 7)
May-31 Cum. Total = 92 (not div by 7)
Jun-30 Cum. Total = 122 (not div by 7)
Jul-31 Cum. Total = 153 (not div by 7)
Aug-31 Cum. Total = 184 (not div by 7)
Sep-30 Cum. Total = 214 (not div by 7)
Oct-31 Cum. Total = 245 (Div by 7!!)

Thus, 245 days after Fri Mar 13th will not only be the 13th of Nov but it will also land on a Friday!
Why? Because, 245 is the cumulative total of the number of days in the 8 months starting in Mar but it is also a multiple of 7. No simple formula here, just grinding it out.

(1) Is 3 the maximum number of Friday the 13ths in any calendar year?
Ans: Yes!
(2) When is the next calendar year in which this 3-peat (three Friday 13ths in one calendar year) will occur?
Ans: See below!
(3) Is 1 the minimum number, i.e, could there be a calendar year in which there are no Fri the 13ths?
Ans: See below!
(4) In which months could a 3-peat occur in a non-leap year? A leap year?
Ans: See below!
(5) Related to (4): 31+29+31 = 91: What does this tell you about Friday 13ths in a leap year?
(6) Other questions: From the students!

The following is from the excellent Wikipedia article on Friday the 13th...

The following months have a Friday the 13th:

Month Years Dominical
Letter
January 2006, 2012, 2017, 2023 A, AG
February 2004, 2009, 2015, 2026 D, DC
March 2009, 2015, 2020, 2026 D, ED
April 2001, 2007, 2012, 2018 G, AG
May 2005, 2011, 2016, 2022 B, CB
June 2003, 2008, 2014, 2025 E, FE
July 2001, 2007, 2012, 2018 G, AG
August 2004, 2010, 2021, 2027 C, DC
September 2002, 2013, 2019, 2024 F, GF
October 2006, 2017, 2023, 2028 A, BA
November 2009, 2015, 2020, 2026 D, ED
December 2002, 2013, 2019, 2024 F, GF

The following years have Fridays the 13th in these months:

Year Months Dominical
Letter
2001 April, July G
2002 September, December F
2003 June E
2004 February, August DC
2005 May B
2006 January, October A
2007 April, July G
2008 June FE
2009 February, March, November D
2010 August C
2011 May B
2012 January, April, July AG
2013 September, December F
2014 June E
2015 February, March, November D
2016 May CB
2017 January, October A
2018 April, July G
2019 September, December F
2020 March, November ED
2021 August C
2022 May B
2023 January, October A
2024 September, December GF
2025 June E
2026 February, March, November D
2027 August C
2028 October BA

This sequence, here given for 2001–2028, repeats every 28 years from 1901 to 2099. The months with a Friday the 13th are determined by the Dominical letter (G, F, GF, etc.) of the year. Any month that begins on a Sunday will contain a Friday the 13th, and there is at least one Friday the 13th in every calendar year.

The longest period that can occur without a Friday the 13th is fourteen months, either from July to September the following year (e.g. in 2001/2002 and 2012/13), or from August to October in a leap year (e.g. in 2027/28).

Patterns for non leap-years:

First month occurring Second month Third month
January October
February March November
April July
May

June

August

September December

Patterns for leap years:

First month occurring Second month Third month
January April July
February August
March November
May

June

September December
October

## Thursday, February 5, 2009

### Odds and Evens 2-6-09: Contest Updates, ADP Algebra EOC Tests, "Numb and Numberer", a MathNotations Podcast?

MathNotation's First Math Contest
The Feb 3rd contest is 'virtually' over! We had a dozen schools participate including high schools, middle schools, a HomeSchooling team, a math fraternity team and a team from the UK! Our British team has had to delay the contest until they dig out of the deep snow that's been blanketing and paralyzing the UK for several days. I sure hope I am not in some way responsible for that!

The contest has been well-received although much of it proved too advanced for our middle schoolers. I will post results and selected problems in a few days after I sort it all out. I am planning on one more free contest in the spring. This one will probably be restricted to secondary teams. If interested, let me know early on. I am also planning 4 contests for the 2009-10 school year. Details about dates, registration and fee will be forthcoming.

"Is trillion the new billion?"
What are the odds that a CNN feature story appeared a few days after the Super Bowl post I published - Was the First Super Bowl More or Less Than a BILLION Seconds Ago?

Heres' an excerpt from this wonderful piece on CNN.com:

"To put a trillion dollars in context, if you spend a million dollars every day since Jesus was born, you still wouldn't have spent a trillion," McConnell said.

CNN checked McConnell's numbers with noted Temple University math professor and author John Allen Paulos.

"A million dollars a day for 2,000 years is only three-quarters of a trillion dollars. It's a big number no matter how you slice it," Paulos said.

Here's another way to look at it.

"A million seconds is about 11½ days. A billion seconds is about 32 years, and a trillion seconds is 32,000 years," Paulos said. "People tend to lump them together, perhaps because they rhyme, but if you think of it in terms of a jail sentence, do you want to go to jail for 11½ days or 32 years or maybe 32,000 years? So, they're vastly different, and people generally don't really have a real visceral grasp of the differences among them."

Everyone is tossing around the words million, billion and trillion. With the national debt now topping \$10 trillion, following a \$700 billion bank rescue and proposed \$800 billion-plus stimulus package, have we become numb to the numbers?

Prof. Paulos is making an excellent case here for our middle schoolers developing better sense about large numbers. This is another view of the Number Sense standards which have been promoted for over two decades. Ah, the Power of Ten! Gee, that would be a cool name for a game show...

Update on ADP Algebra I, II EOC Tests
Do you frequently check the Achieve website to get the latest info on these tests, revised benchmarks and latest developments. For a current overview on the Algebra I test, look here.
I don't yet see released items or a set of sample questions but there is some very helpful information there, in particular the Algebra I Expected Knowledge document you can download. This can serve as the basis for curriculum development and provides sorely needed consistency. It will help to address questions like: Should we still teach those mixture problems? How much emphasis should we place on factoring quadratic trinomials?

MathNotations Podcast

Ok, what's this nonsense about podcasting? Another venture that I will try and not follow through on? Perhaps, but I'm never afraid to challenge bold frontiers that people my age are not supposed to consider! I would like to offer MathNotations visitors another way to connect with issues in math education. Once I get this set up, I'll let you know. There are a few technical obstacles I need to overcome but I'm getting close.