Factoring the time

I stumbled upon this comic that you might enjoy... factoring the time (from xkcd.com).

Carnival time: Math Teacher's at Play

Head on over to Math Teachers At Play #29 carnival to read a nice assortment of posts on math education!

Math tricks by a silly guy

A short youtube video where Kjartan Poskitt shows some math tricks. He's funny! Enjoy!

The equal sign problem

An interesting piece of research has just come out on the misconceptions with the equal sign (=).

Students' understanding of the equal sign not equal

According to the research, US students exhibit this misconception much more often than students in other countries. It has to do with thinking of the = sign as an operator. Kind of like thinking that = means "to do" the operation.

For example, a student with that misconception tends to solve the problem

7 + 6 = ____ + 2 

by adding 7 + 6, and placing the answer on the empty line.

The correct way is of course to think of the equality: 7 + 6 equals 13, so the other side has to equal 13 too. 11 fulfills this little equation:

7 + 6 = 11 + 2

I have known of this problem for years, and have tried to include problems in my Math Mammoth books to help children NOT to develop this wrong idea. For example, children solve


200 + 50 + 6 = ____ + 200 + 50 in the place value section.

Or, I use problems where they have to put either <, >, or = in between (one the line here, but I like to use boxes in the books):

20 + 9  _______ 90 + 2

8 + 6   ________  7 + 7


Or, just simple missing addend problems from the very start (1st grade):

3 + _____ = 5.


Remember, students exhibiting the misconception would add 3 and 5, and put 8 on the empty line. But we can teach kids to think of this problem as "3 and how many more makes 5". It is a starting point in understanding the equal sign in the correct way.

Then they should also (later on) encounter the same problem this way:

5 = ____ + 3

And other variations.

Math Mammoth Geometry 2

I have just finished writing the material for Math Mammoth Geometry 2 book. The material in it is suitable for grades 6-7. Download price is $5.80.

The main topics in the book include:

* angle relationships
* classifying triangles and quadrilaterals
* angle sum of triangles and quadrilaterals
* congruent transformations, including some in the coordinate grid
* similar figures, including using ratios and proportions
* review of the area of all common polygons
* circumference of a circle (Pi)
* area of a circle
* conversions between units of area (both metric and customary)
* volume and surface area of common solids
* conversions between units of volume (both metric and customary)
* some common compass-and-ruler constructions.

I've included several complete lessons from the book as samples (PDF). Feel free to download these and use with your students!

Angles in Polygons
Review: Area of Polygons, 1
Surface Area

Besides those, there are two other sample pages:

Area and Perimeter Problems
Basic Compass and Ruler Constructions, 1

What is next?

• See more information
• Purchase a download at Kagi
• Purchase a download at Currclick

Review of Harold Jacobs Geometry

I have just posted a comprehensive review of this book that is popular among homeschoolers for a high school geometry course. Click to read:

Review of Harold Jacobs Geometry book

Math assessment and placement

My daughter just completed the end-of-year math test for 4th grade. She scored 82%. She missed doing one question (just forgot), made a few careless mistakes, and then missed several in the measuring unit section because she didn't remember how many ounces are in a pound or how many grams in a kilogram. So we need to review some of that.

But overall, I am happy with the results, because (and I knew this beforehand too) she understands the concepts well! That is the most important thing. It's always easy to review some forgotten facts (such as measuring units), but when child has not understood the main concepts, the "patch-up" work is more tedious.

I have provided these Math Mammoth end-of-year tests on my site as free downloads so that people can use them as placement tests or for general math assessment. I often have people email me about their kids' results, and based on that, I feel those tests are working fine.

I have also collected a few other math assessment resources on this page, notably the yearly tests from Texas, Florida, and California (which are free) and a few commercial resources. Note: in my opinion, California's math standards are a bit too advanced, so use care when using their tests.

Some parents are against testing, but I feel testing for assessment is often needful in order to know what the child knows and doesn't know. The tests are like a "diagnostic toolbox" for me when I need to guide parents in what Math Mammoth books they might need for their children. So the purpose is not to "put on the pressure", but just to find out.

Kenken game for summer fun

As most of you are taking a break from math or school work, here's a little (addictive) math game to play online or as printed version: Kenken.

In it, you have to place the numbers in the grid kind of like in Sudoku so that no number appears twice in the same row or column, BUT there's an additional twist: it gives you "cages", and the numbers within a particular cage have to work to a given answer with a given math operation (either addition, subtraction, multiplication, or division).

KenKen practices logical thinking and is, I think, more fun than Sudoku.

It's easier to understand if you go see and try it yourself. The smaller sizes, such as 4x4 game, are great for kids, and the larger ones are good for us adults or older students.

• Kenken.com has nice Kenken puzzles online plus instructions, but only one for each size.

• MathDoku.com has an unlimited number of Kenken puzzles to play online in three sizes and several difficulty levels.

My favorite music

This is a bit different entry from the norm, and if you're not interested in music (or oldies music), just ignore it. (I realize people's musical tastes vary tremendously.) I just wanted to share a bit of news of my favorite, 24K Gold Music Shows, and their new YouTube channel. They mainly play music from 50s and 60s; that is, oldies music.

(Well, I do also like classical music pretty well -- I played piano in my youth for 13 years, and still occasionally do at home.)

You can now see 24K Gold music videos at YouTube. For example (click on the song links to see these in high density):


Cara Mia (my favorite!):


Love Can Build a Bridge (a beautiful ballad with a strong emotion):


Or something faster such as Elvis' Burning Love:




Johnny B Goode



See more videos - or subscribe at their channel page.

Math Jokes 4 Math Folks book

I recently received Math Jokes 4 Mathy Folks from the author, Patrick Vennebush. This is a very comprehensive collection of math-related jokes that all "mathy" people will definitely enjoy, and math teachers could use this book to enliven their lessons.

I have seen several of the jokes on the Internet, but never such a large collection.

The jokes are categories into chapters such as

• One-Liners, ("A hungry clock goes back four seconds.")

• Graphic Jokes, (For example, "Cube Roots" picture you see on the cover of the book.)

• Three Dudes, (An engineer, a mathematician, and a chemist are...)

• Conversion Chart, (10⁹ antics = 1 gigantic, or 454 graham crackers = 1 pound cake)

• Professions,("The secretary of defense informed the president, 'Yesterday, three Brazilian soldiers were killed. 'Oh, no!' the president exclaimed. ... 'How many is a brazillion, anyway?' ")

And so on.

In each section, the jokes that require the least math knowledge to understand are first, and then the material "advances". People who have studied math in college will get the most out of it, but there are joke for every level.

Please note the author has included a few bathroom jokes and a few slightly dirty ones - if you don't like those, they can easily be marked over.

Algebra 1 curriculum advice

I have just finished writing a LONG article on homeschool algebra 1 recommendations and advice. It took me quite many hours to write and research.

Questions about what to do for algebra 1 have become one of the "frequently asked questions", so I decided to write down something that I can refer people to, from now on.

I realize you may have different opinions and even suggestions for algebra curriculum in homeschool, so if you let me know, I'm willing to look into other possibilities not mentioned in the article.