hyperpape wrote:And with regard to math (or most areas of knowledge): you often don't see where it's useful until you really understand it, at which point it shapes every aspect of how you see a problem. So I think most people who think they wouldn't get much out of knowing math probably don't realize what they are missing.
The other problem is that most mathematical thinking you do in everyday life revolves around having good intuitions and informally stated problems. School math tends to do a bad job of cultivating that sort of thought.
When I saw the title of this thread, I thought, Me!

hyperpape, you make a good point about the value of mathematical thinking and how, unfortunately, school math does not do a good job of imparting it. One reason, OC, is that most secondary school teachers are not very good at it, either. If they were, they would have better paying job options.
A wonderful example of mathematical thinking is the famous story of young Gauss in the first grade of a one room schoolhouse. The teacher, probably needing a break, gave the students the task of adding the numbers from 1 to 100. In a couple of minutes Gauss handed in his paper. What he had done was to add 1 to 100 to get 101, then add 2 to 99 to get 101, etc. He had done that 50 times and the sum of 50 101s is 5050. Done!
That was not only very clever, it was an example of divergent thinking. Take that, Weather Woman!

Those of us with a little algebra can derive the expression, N(N+1)/2. Those of us with a little geometry can take a triangle like
*
**
***
****
*****
and fold it to get this rectangle
*****
*****
*****

How and why do the algebraists do that?
Why? Because it's fun. Take that, Weather Woman!
How? Let me address the more general question of algebraic thinking.
DrStraw has mentioned the importance of the idea of equality. Rearranging the *s in the triangle did not change how many there were. That number remained equal for both figures. When Gauss rearranged the addends that did not change the sum.
I think that one of the most valuable ideas in algebra is that of an unknown. Now, in real life there are lots of things that we do not know. The unknown is vast. It is a real cognitive leap, in the face of that vastness, to think about a specific unknown, when we may have no guarantee that it exists.
Closely related to the idea of an unknown is the idea of a variable. To find an unknown we may set up an equation with a variable and solve the equation for that variable.
Another important idea is that of a function. One variable may be the function of another variable.
There is a lot more to algebraic thinking, OC, but one thing that algebraists do is to look for functions. Given the problem of adding the numbers from 1 to 100, the algebraist replaces the 100 with a variable (N) and looks for a function of N which is equal to the sum of the numbers from 1 to N. It is N(N+1)/2. Voila! (Well, not quite voila, you have to prove it.)
This way of thinking, of taking the known and leaping into the unknown, looking for functions and relations, is powerful and often practical. It is not only problem solving behavior, it is problem seeking behavior. It is something that algebra courses could foster, and, IMO, should foster.
