Math Is Fun Forum

See under "Quick Post" there is a little link that says "Smilies" - that lists them.

"Whats up with that?"

Vertices: Plural of vertex

The vertex is just a corner point.

A cube has 8 vertices.

An egyptian pyramid would have 5 (one at the top, and each corner of the base)

Exactly - I had to delete a few "shutups". This isn't doing anyone any good.

OK, OK, we probably need a special forum for blonde jokes.

Maybe call it "hair-colour-challenged jokes" 

Arrggghhh indeed !

Let me put my thinking cap on here ...

You can read up on Mean and Standard Deviation if you want to, first.

Well, you said "normal" distribution. That is a special word that says it follows a certain well-defined pattern on a graph that looks like a bell. (Funny that "normal" means it is special ...)

You can look at the curve here

First step is to figure how many standard deviations (80 in your case) that each value is from the mean (120 in your case).

Let us work on your examples:

i) below 100   ==>  100 is 20 away from the mean of 120, so it is 20/80 = 0.25 standard deviations away.
ii) above 130  ==>  130 is 10 away from the mean of 120, so it is 10/80 = 0.125 standard deviations away.

The next step is to look up these values (0.25 and 0.375), which are called "z-scores", in a table. Yep, you gotta look em up, unless you have them as a special function on your calculator or software.

Looking up these values, I get:

0.25: 0.0987
0.12: 0.0478

That means that 0.0987, or 9.87%, of the population are between the mean (120) and 100
And that 0.0478, or 4.78% are between the mean and 130

The rest is just figuring what the question asked: above, below, between?

The first question says "below 100" - well, we know that 9.87% are between 100 and 120, and 50% must be greater than 120 (because 120 is the mean), so 59.87% are GREATER, and therefore 41.2% must be LESSER, or below!

Likewise "above 130" can be figured out to be 45.2%

All the others can be worked out in a similar way, and I leave that up to you ... !

Coca Cola is real:

It kinda grows on you ... is it quod its easier to type, or quod it just seems to fit?

What do you think Zach ... it isn't AOL-ish.

Well there you go, Jessamy DOES know some maths ...

Thank you. I did not mean that his line of sight passed through the very top, I merely said "grazes the upper surface" (ie a tangent)

Yes, it needs triangles to solve. And the spike's height can likewise be solved.

Could you crunch the numbers, and see if you agree with my 8.24m distance to centre line of dome?

Oh, and if you can spare the time you are most welcome to drop by the forum every so often and help with some of the "Help Me!" problems.

I wouldn't go messin' with Mr T ....

There, I warned you.

Who cares? We do!

So sorry, Jessamy. You are in a difficult position, aren't you? You need to do maths, and it is important if you want a career, but you don't like it.

You say "half the things you actually learn you will never need anyway". But which half? If you want to do Business, Medicine, Engineering, Political Science, Carpentry, Electrical Trade, or most any worthwhile career, you will need to do lots of maths.

I believe there is an underlying reason you hate maths, and it is not the fault of maths itself, but more to do with how you have learned it.

Somewhere along the way it became hard for you, and every year it is just gets harder.

You need to go back to where it was easy and build yourself back up again.

Maths isn't easy, but it is CERTAIN.

Luckily for you there are now great resources to help students on the internet.