jbo5112 wrote:5th grade field trip to planetarium (paraphrase): "We calculate how far away a star is based on how big it looks and how big it actually is. We calculate how big a star actually is based on how far away it is and how big it looks." The first time he made these statements were in different sections of his lecture, but I still caught it and called him on it. He then made both statements within a minute or two, apparently not realizing that you can't solve for 2 variables with his 1 pseudo-equation. The explanation from the planetarium employee was reduced to "we also have other methods we use", and he quickly moved on after a 5th grader exposed his stupidity.

You're being rather harsh on him. While it's true that you can't solve for 2 variables with one equation, it's

entirely correct that "we also have other methods we use" is how they solve that problem. You didn't expose his stupidity as much as mention that he spoke wrong, and he explained very quickly what mistake he had made. I'll agree that it might not have satisfied you, but he's not being stupid.

merlanai wrote:I wonder if anybody else was taught how to taught how to count to 100 on their fingers, and use the same technique to be able to do a long series of simple addition/subtraction/multiplication/division as fast as a person could read it off to you.

36 divided by 6 plus 5 times 2 - 2 divided by 5 minus 2 minus 2 plus 10 times 5 plus 6 divided by 8 plus 2 EQUALS:

That might be a good way to teach quick arithmetic, but it anathema to good order-of-operations. When someone reads that out as fast as they can, they can't make indicative pauses, so the answer to that task ends up being 62.35, which I understand to be difficult to display with fingers...

Seriously, I hate that nobody bothered to explains order-of-operations to me in primary school. It was the particular brilliance of my teachers/the Ministry of Education to then insist on including that on the tests. For that matter, the clarity of mind that is required to give out a test three months before the year ends, that covers everything on the curriculum that year.

Of course, in the last year of primary school, I was outsmarting my maths teacher.

"How do I divide two decimal numbers?"

"For such difficult questions, we use a calculator."

Then I went home, complained to my parents, and was told how to do it. Difficult? DIFFICULT? I've never seen a simpler way to solve a question like that, and the knowledge of how to solve it would have been

invaluable to the rest of the class once they started to learn algebra.

jpers36 wrote:Forget that, I can count to 1024 on my two hands.

Yes, yes, I guess you

can if you want to, but it looks so much more beautiful if you stop at 1023.

Grant10k wrote:It's all fun and games until you get to 132.

People always looked strangely at me when I was counting something and reached 4 or 20. Eventually I learnt to just ignore it or keep my hands out of sight.

Fun story. A few weeks ago we were learning about electromagnetic induction and such things in class, and we were handed a stack of previous exam papers that we could use to study. I leaf through the thing and arrive at a question:

"induce a current in a copper ring, using only insulated wire, a variable resistor, and a cell"

So, I dig into the question and realize that I need to exploit Lenz' Law (where the change in magnetic field strength will be opposed by a proportional but opposite magnetic field) by creating a solenoid from the wire, and attaching the variable resistor and the cell to it. I can then aim the solenoid along the perpendicular to the plane of the copper ring, and by varying the resistor, I can create a varying magnetic field strength. This varying magnetic field strength will then create and opposed magnetic field along the perpendicular to the plane of the copper ring, and it will induce a current in the copper ring.

Simple, right?

Well, it turns out that the answer key just said to wrap the wire around the copper ring. Except that is wrong. That would induce a magnetic field in the copper ring, but no current. Peeved, I turn to the student next to me and raise the question, and he looks at it and has the same realization. The key is wrong. Completely utterly wrong. I even, still somewhat doubtful, talk to a theoretical physicist, and he tells me that the key was wrong.

Of course, he also had a much simpler solution: as long as you're not on the magnetic North or South pole, place the copper ring vertical on a table and spin along the axis normal to the Earth's surface...