Maria's Math News, Vol. 60, February 2012

I love teaching, and I love math. This newsletter is my way of reaching out and helping you to teach it, too.

Are your kids developing good study skills?

The ability to focus and work independently—study skills—has been shown to be one of the strongest pre-cursors to later success in school.

K5 Learning is an
online reading and math program that helps kindergarten to grade 5 students develop reading, math and study skills. Kids work independently as they proceed at their own pace through K5's 3,000 award winning reading and math activities.

K5's 14-day free trial includes full access to the program and free reading and math assessments. Don't forget to enter MM2012 as your promotional code!

Welcome to February! I hope I found "something for everyone," again!


1. Math Mammoth sale notices
2. Triangle puzzle - equal areas
3. Vi Hart and mathematical doodling
4. Compound interest
5. Geometry videos
6. Tidbits

1. Math Mammoth sale notices

Homeschool Buyers Co-op will run a (traditional) group buy for Math Mammoth through the month of March.

And for those of you that missed my three-day sale in January, I'll run another in late February! But no, this won't become a monthly habit after that.

2. Triangle puzzle - equal areas

triangle puzzle

Basically, we have a triangle DFE inside a rectangle, dividing the rectangle into various triangles. And, the three areas of fainter color are equal. That is, the area of the triangle DAE = area of the triangle EBF = area of the triangle FCD. (Notice the image is not drawn to scale at all.)

And, we're asked to solve the RATIOS AE : EB and BF : FC.

The solution is posted here.

3. Vi Hart and mathematical doodling

I just learned about Vi Hart's "doodling in math class" videos.

Vi calls herself mathemusician - and definitely, she's a talented and smart gal! I'm sure you'll enjoy her videos (as long as you can follow her super fast speeaking). Here are some that I enjoyed:

Doodling in Math: Spirals, Fibonacci, and Being a Plant [1 of 3]
Doodling in Math: Spirals, Fibonacci, and Being a Plant

(Also, here's a link to learn more about Fibonacci numbers in nature, so you can read about it at a slow pace : )  )

Binary Hand Dance was pretty cool too!
Binary Hand Dance

Her series of "mathematical doodling" videos have become somewhat of a viral success. Here's one more:

Doodling in Math Class: Infinity Elephants
Doodling in Math Class: Infinity Elephants

You can also see these three videos on my blog.

4. Compound interest

Someone sent me in a question concerning compound interest...
Please send me the formula for compound interest and explain line by line.

p(1 + rate)3

What does the 1 stand for and must you add it to the rate of say 10%?

100(1+10)3 years = ???

Obviously I am looking for a basic course?
The formula that this person is using is correct... the formula for compound interest is

A = p(1 + r)t

but this formula doesn't give us the amount of interest -- it gives us the amount of money you would withdraw after t years. In the formula, p is the original principal, r is the interest rate, and t is the time in years.

However, we cannot put the interest rate in as he did. If r = 10%, then r = 0.1 must be used in this formula. In other words, FIRST convert your percentage into a decimal.

Read more

5. Geometry videos

I have expanded the list of 4th-5th grade geometry videos that are available for you to watch! The topics include now:
Enjoy! Hope they are of help.

6. Tidbits

Feel free to forward this issue to a friend/colleague! Subscribe here.

Till next time,
Maria Miller
Newsletter Archives  —  Math Mammoth books  —  Free worksheets  —  Curriculum guide
Lessons & teaching guides  —  Math product reviews  —  Online games & tutorials