Radiation Sanity Chart

Posted on by Denise Gaskins

With news reports of radiation from Japan being found from California to Massachusetts — and now even in milk — math teachers need to help our students put it all in perspective.

xkcd to the rescue!

Pajamas Media offers a brief history of radiation, plus an analysis of our exposure in Banana Equivalent Doses:

And the EPA offers a FAQ:

[T]he levels being seen now are 25 times below the level that would be of concern even for infants, pregnant women or breastfeeding women, who are the most sensitive to radiation… At this time, there is no need to take extra precautions… Iodine-131 disappears relatively quickly in the environment.

— Centers for Disease Control and Prevention (CDC)
pages 4-5 of EPA FAQ

[Hat tip: Why Homeschool.]

Math Teachers at Play #35

Posted on by Denise Gaskins
35 is a tetrahedral number

Welcome to the Math Teachers At Play blog carnival — which is not just for math teachers.

Do you enjoy math? I hope so! If not, browsing these links just may change your mind. Most of these posts were submitted by the bloggers themselves; others are drawn from my overflowing Google Reader. From preschool to high school, there are plenty of interesting things to learn.

Let the mathematical fun begin…

Continue reading Math Teachers at Play #35

Babymath: Story Problem Challenge III

Posted on by Denise Gaskins

<a href="http://www.flickr.com/photos/goetter/2352128932/"Photo by Raphael Goetter via Flickr

Alex and Leon enjoyed their baby sister, but they were amazed at how much work taking care of a baby could be. One particularly colicky night, everyone in the family took turns holding the baby, rocking the baby, patting her back, and walking her around before she finally succumbed to sleep.

Then Alex collapsed on the couch, and Leon sank into the recliner. They teased each other with these story problems.

Continue reading Babymath: Story Problem Challenge III

Probability Issue: Hints and Answers

Posted on by Denise Gaskins

Remember the Math Adventurer’s Rule: Figure it out for yourself! Whenever I give a problem in an Alexandria Jones story, I will try to post the answer soon afterward. But don’t peek! If I tell you the answer, you miss out on the fun of solving the puzzle. So if you haven’t worked these problems yet, go back to the original posts. If you’re stuck, read the hints. Then go back and try again. Figure them out for yourself — and then check the answers just to prove that you got them right.

This post offers hints and answers to puzzles from these blog posts:

Continue reading Probability Issue: Hints and Answers

Rate Puzzle: How Fast Does She Read?

Posted on by Denise Gaskins


[Photo by Arwen Abendstern.]

If a girl and a half
can read a book and a half
in a day and a half,
then how many books can one girl read in the month of June?

Kitten reads voraciously, but she decided to skip our library’s summer reading program this year. The Border’s Double-Dog Dare Program was a lot less hassle and had a better prize: a free book! Of course, it didn’t take her all summer to finish 10 books.

How fast does Kitten read?

Continue reading Rate Puzzle: How Fast Does She Read?

Hobbit Math: Elementary Problem Solving 5th Grade

Posted on by Denise Gaskins

[Photo by OliBac. Visit OliBac’s photostream for more.]

The elementary grades 1-4 laid the foundations, the basics of arithmetic: addition, subtraction, multiplication, division, and fractions. In grade 5, students are expected to master most aspects of fraction math and begin working with the rest of the Math Monsters: decimals, ratios, and percents (all of which are specialized fractions).

Word problems grow ever more complex as well, and learning to explain (justify) multi-step solutions becomes a first step toward writing proofs.

This installment of my elementary problem solving series is based on the Singapore Primary Mathematics, Level 5A. For your reading pleasure, I have translated the problems into the world of J.R.R. Tolkien’s classic, The Hobbit.

UPDATE: Problems have been genericized to avoid copyright issues.

Continue reading Hobbit Math: Elementary Problem Solving 5th Grade

Best Articles about Solving Word Problems

Posted on by Denise Gaskins


[Photo by scui3asteveo.]

I’m still working on that Best of Blog page. [It’s done! :D] Here are the 20 best Let’s Play Math! blog articles about solving word problems (also known as story problems)…

Solving Word Problems

More recent posts tagged ‘Word problems’

Bar Diagrams Help Students Think

More recent posts tagged ‘Bar diagrams’

Other Post in the Best of Blog Series

Update: My New Book

You can help prevent math anxiety by giving your children the mental tools they need to conquer the toughest story problems.

Check out Word Problems from Literature: An Introduction to Bar Model Diagrams—now available at all your favorite online bookstores!

And there’s a Student Workbook, too.

Word Problems from Literature

Posted on by Denise Gaskins

[Photo by Passion of Bilwa.]

I’ve put the word problems from my elementary problem solving series into printable worksheets:

Continue reading Word Problems from Literature

The Cookie Factory Guide to Long Division

Posted on by Denise Gaskins

[Photo by scubadive67.]

Help! My son was doing fine in math until he started long division, but now he’s completely lost! I always got confused with all those steps myself. How can I explain it to him?

Long division. It’s one of the scariest of the Math Monsters, those tough topics of upper-elementary and middle school mathematics. Of all the topics that come up on homeschool math forums, perhaps only one (“How can I get my child to learn the math facts?”) causes parents more anxiety.

Most of the “helpful advice” I’ve seen focuses on mnemonics (“Dad/Mother/Sister/Brother” to remember the steps: Divide, Multiply, Subtract, Bring down) or drafting (turn your notebook paper sideways and use the lines to keep your columns straight).

I worry that parents are too focused on their child mastering the algorithm, learning to follow the procedure, rather than on truly understanding what is happening in long division.

An algorithm is simply a step-by-step recipe for doing a mathematical calculation. But WHY does the algorithm work? If our students could understand the reason for the steps, they wouldn’t have to work so hard on memory tricks.

Continue reading The Cookie Factory Guide to Long Division