## Number Bonds = Better Understanding

[Rescued from my old blog.]

A number bond is a mental picture of the relationship between a number and the parts that combine to make it. The concept of number bonds is very basic, an important foundation for understanding how numbers work. A whole thing is made up of parts. If you know the parts, you can put them together (add) to find the whole. If you know the whole and one of the parts, you take away the part you know (subtract) to find the other part.

Number bonds let children see the inverse relationship between addition and subtraction. Subtraction is not a totally different thing from addition; they are mirror images. To subtract means to figure out how much more you would have to add to get the whole thing.

## I’m Your Birthday Present. Can You Find Me?

One of our favorite family traditions for young children is the “hidden present.” Every year, one birthday present is hidden somewhere in the house, with the clue placed in an envelope to be opened after all the other presents are unwrapped.

## 2007 Mathematics Game

The Math Forum: 2007 Mathematics Game will be a tricky one:

Use the digits in the year 2007 and the operations +, -, x, ÷, sqrt (square root), ^ (raise to a power), and ! (factorial), along with grouping symbols, to write expressions for the counting numbers 1 through 100.

• All four digits must be used in the expression.
• Only the digits 2, 0, 0, 7 may be used.
• Multi-digit numbers such as 20, 207, or .02 MAY be used this year.
• The square function may NOT be used.
• The integer function may NOT be used.

## Negative Numbers for Young Students

[Rescued from my old blog.]

Would you like to introduce your students to negative numbers before they study them in pre-algebra? With a whimsical number line, negative numbers are easy for children to understand.

Get a sheet of poster board, and paint a tree with roots — or a boat on the ocean, with water and fish below and bright sky above. Use big brushes and thick poster paint, so you are not tempted to put in too much detail. A thick, permanent marker works well to draw in your number line, with zero at ground (or sea) level and the negative numbers down below.

## Harmonic Series Quotation

If you’d like to start your week with a laugh, here’s a great quote:

Today I said to the calculus students, “I know, you’re looking at this series and you don’t see what I’m warning you about. You look and it and you think, ‘I trust this series. I would take candy from this series. I would get in a car with this series.’ But I’m going to warn you, this series is out to get you. Always remember: The harmonic series diverges. Never forget it.”

—Rudbeckia Hirta
Learning Curves Blog: The Harmonic Series
quoting Alexandre Borovik

## Order of Operations

[Rescued from my old blog.]

Marjorie in AZ asked a terrific question on the (now defunct) AHFH Math forum:

“…I have always been taught that the order of operations (Parenthesis, Exponents, Multiplication, Division, Addition, Subtraction) means that you work a problem in that order. All parenthesis first, then all exponents, then all multiplication from left to right, then all division from left to right, etc. …”

Many people are confused with order of operations, and it is often poorly taught. I’m afraid that Marjorie has fallen victim to a poor teacher — or at least, to a teacher who didn’t fully understand math. Rather than thinking of a strict “PEMDAS” progression, think of a series of stair steps, with the inverse operations being on the same level.

## It’s Elementary (School), My Dear Watson

[Rescued from my old blog.]

From Time magazine, June 18, 1956:

“[M]athematics has the dubious honor of being the least popular subject in the curriculum… Future teachers pass through the elementary schools learning to detest mathematics… They return to the elementary school to teach a new generation to detest it.”

Quoted by George Polya in How to Solve It. I finally got my very own copy of this excellent book, so I can quit pestering the librarian to let me order it from library loan again…

Blogger Rudbeckia Hirta teaches math to pre-service teachers, and it seems that not much has changed since 1956. Hirta says the test answers shown were representative of her class — for instance, 25% of her students missed the juice problem. Too bad these students never read Polya’s book, in which he discusses a four-step method for solving problems. Step four is to look back and ask yourself whether the answer makes sense. Good advice!

## Our Tax Dollars at Work

Well, the new year has come, and it’s time to start gathering up receipts and thinking about tax forms.

Would you like to know that our tax dollars are doing good in the world? The National Science Foundation has spent many millions developing and promoting “reform” math textbooks, with encouragement from the U.S. Department of Education. Surely our public schools will now rise out of the doldrums and surge ahead in mathematical achievement, right?

Try for yourself this problem from one of the more famous/infamous of the reform math textbooks:

Can you find the slope and y-intercept of this equation?

10 = x – 2.5

And then check out this editorial[editorial has disappeared] at edspresso.com. You’ll be amazed at the answer!

Update: Checking on back-links, I discovered that this page had gone AWOL, so I’ll give you the “answer” from the teacher’s manual. The “slope” is 1 and the “y-intercept” is -2.5, according to Connected Math. Unfortunately, this equation actually describes a vertical line (undefined slope) at x=12.5 (never touches the y-axis).

Doesn’t bode well for “CMP helps students and teachers develop understanding of important mathematical concepts…”

## Set Daily Puzzle

The spring semester of homeschool co-op classes starts tomorrow, and I still have a couple of handouts to prepare and several pages of notes to go over in preparation. So naturally, I find myself flitting from here to there on my computer, browsing new links and cleaning out the old.

As the saying goes:

“I used to be an amateur crastinator, but now I’ve turned pro.”

In a dusty pile of long-neglected bookmarks, I rediscovered this treasure:

Set Daily Puzzle

I love this game!