|
|
| Author |
Message |
aruba
|
|
The Math Item
| 
Aug 7 16:20 UTC 1994 |
Enter questions about math here.
|
| 47 responses total. |
alfee
|
|
response 1 of 47:
|
Aug 13 17:47 UTC 1994 |
I am preparing to take the GRE in the spring in order to apply for graduate
school. My weak area is math--on the SAT, I got a perfect verbal score and
a 650 on math. My question is: can anyone recommend a decent way for me
to brush up on my math skills? I took a formal math course last in 1988.
I'm looking for teach-yourself type material, preferably user-friendly. To
be honest, I feel about math the way some feel about an abusive parent: we
have not had a very productive relationship. Any suggestions?
|
aruba
|
|
response 2 of 47:
|
Aug 13 21:53 UTC 1994 |
It's been a while since I took the GRE - what kind of math is on it?
|
alfee
|
|
response 3 of 47:
|
Aug 14 02:05 UTC 1994 |
Basic and advanced algebra, geometry, and some trig. Not really any basic
arithmetic-type-stuff, which I guess I should be proficient at by now.
|
aruba
|
|
response 4 of 47:
|
Aug 14 03:23 UTC 1994 |
Brenda is a good person to answer this, since she has been brushing up
on her math lately.
|
rcurl
|
|
response 5 of 47:
|
Aug 14 05:18 UTC 1994 |
There must be GRE "prep" manuals. See if you can find one of those. People
here can help the most on specific difficulties.
|
srw
|
|
response 6 of 47:
|
Aug 14 06:12 UTC 1994 |
Try Border's for GRE Prep manuals.
|
popcorn
|
|
response 7 of 47:
|
Aug 14 17:03 UTC 1994 |
This response has been erased.
|
alfee
|
|
response 8 of 47:
|
Aug 14 19:00 UTC 1994 |
I ran out and got two prep books--one Arco and one Barrons, and they both look
good. Wish I had a Border's down here!. I'll be back with specific questions,
believe me.
|
ryan1
|
|
response 9 of 47:
|
Aug 29 18:50 UTC 1994 |
can someone please help me on this one.
3 men chech into a very cheap motel. They decid to share a room.
Each man hands $10 to the person at the front desk. Later the person realises
that rooms only cost $25. He gives $3 back and keeps the extra $2 so there
wouldn't be an argument amongst the 3 men.
So...each man paid $10 minus the $1 recieved back=$9
9x3 men =$27 plus the $2 the person at the desk kept= $29 !
Where is the missing dollar?
|
rcurl
|
|
response 10 of 47:
|
Aug 29 19:15 UTC 1994 |
You are adding incomensurables. The hotel got $25, the men paid $27,
and the clerk ripped off the difference of $2.
|
brenda
|
|
response 11 of 47:
|
Aug 29 19:47 UTC 1994 |
read the iq conf. This exact same item is there, with a ton of responses.
|
rcurl
|
|
response 12 of 47:
|
Aug 29 20:00 UTC 1994 |
Oh! I thought ryan1 really wanted to know! (not).
|
ryan1
|
|
response 13 of 47:
|
Sep 1 22:38 UTC 1994 |
O.K. You figured me out! I was playing a trick on you. I wanted to see how
many responces it would take to figure it out.
|
kerf
|
|
response 14 of 47:
|
Jul 6 22:55 UTC 1995 |
Wow! This math section certainly lacks participation!! Maybe math is
falling into disuse these days? Anyway, to stir the pot (perhaps):
Can anyone tell me the origin and the value of the number known as a
google? I have a general idea of the origin, but cannot recall the
value.
|
rcurl
|
|
response 15 of 47:
|
Jul 7 04:23 UTC 1995 |
A Googol is the decimal number written as 1 followed by 100 zeroes.
That is, 10^100. The name was invented by the nine-year-old (then)
nephew of one Dr. Kasner.
Define G = 10^100. A larger number is the Googolplex, defined
as 10^G.
The apparent lack of participation is due to few people seeking
tutoring. But the tutors are hanging around.....
|
mcpoz
|
|
response 16 of 47:
|
Jul 7 12:29 UTC 1995 |
Where would you use numbers as large as a googol or a googolplex? I read
somewhere (Maybe it was in A Brief History of Time,
Let me start again. Where would you use numbers as large as a Googol or
larger? I read somewhere (I think it was in A Brief History of Time, by
Hawkings) that the mass of the universe was in the range of 10^80 grams.
|
rcurl
|
|
response 17 of 47:
|
Jul 7 17:12 UTC 1995 |
Accepting that, and assuming the universe is mostly hydrogen, that is
10^80 *gram-atoms*. Each gram-atom contains 2.03E23 atoms, giving
2.03E103 atoms in the universe. That is, 2,030 googols. (Or, is that
2.03 kilogoogols?) In regard to the googolplex, my book that discusses
this says:
"One might not believe that such a large number would ever really
have any application, b ut one who felt that way would not be a
mathematician. A number as large as the googolplex might be of real
use in problems of combination."
The article then goes on to describe an example of "combination", or
combinatorial probability, that requires the googolplex. Summarized,
it is that if an object is hung on a string, what is the probability
that it will spontaneously jump above the hanging point (because all
the atoms at that moment vibrated in the same directiion). It can be
shown that this probability lies between (and not outside) the
range (googol)^-1 and (googolplex)^-1. It could, of course, happen
today, as this is probability statement. Watch for it.
|
mcpoz
|
|
response 18 of 47:
|
Jul 7 22:32 UTC 1995 |
Ok, makes sense in terms of probabilities - location of an electron, chemical
reaction, etc.
|
dang
|
|
response 19 of 47:
|
Mar 26 03:47 UTC 1996 |
<sigh> and I had so much hope for this cf. Well, I have a little math
problem that has been nagging me for a while now. I'll post it next
time I'm on from my room.
|
dang
|
|
response 20 of 47:
|
Mar 27 23:58 UTC 1996 |
Okay, here it is. I couldn't find the origional sheet it was assigned
on, but I can reconstruct it. The problem was to derive the
reflection/refraction equations that make a rainbow. It was divided up
into many parts, but one of them was to use fermat's principal to
determine the path followed by the light beam. Thus, an equation was set
up, and the derivative was taken, and the result set to zero to minimize
it. So far, so good. The next part was to solve for x. Now, in order to
solve the question, solving for x is not necessary, and they eventually
took this part out of the project, and all was fine and good. However, I
had gotten to that part, and attempted to solve for x, and couldn't do
it. I spent many hours and many sheets of paper and much frustration on
it, and then was rather ticked when they took it out of the problem. I
since haven't had time to go back to it, but here it is, for the tutoring
cf to worry about for a while:
solve for x, assuming that all other letters are constants:
(n_1*x)/(c(a^2+x^2)^(1/2))-(n_2(d-x))/(c(b^2+(d-x)^2)^(1/2)) = 0
Enjoy!
|
kami
|
|
response 21 of 47:
|
Mar 28 03:41 UTC 1996 |
Michael says, the way it's written, the equation = 0 only when x=0.
|
rcurl
|
|
response 22 of 47:
|
Mar 28 04:47 UTC 1996 |
Are n_1 and n_2 coefficients n1 and n2, and what is the *, which
is not associated with n_2(d-x)? If I take n1 and n2 as coefficients,
and * as multiplication, then I don't agree with #21. c cancels. The
equation expands to forth order polynomial. I do not see a useful way
to factor it.
|
dang
|
|
response 23 of 47:
|
Mar 28 05:45 UTC 1996 |
You're right, n_1 and n_2 are coefficients n1 and n2 ( was attempting to
imply subscript...) and the * is multiplication. The reason it's only
used there is that's the only place where there isn't a paren to imply
multiplication. and, when x = 0, I get -n2*d/(c(b^2 + d^2)^(1/2), not 0.
I came up with the same thing as in the above response, and couldn't for
the life of me solve it. I'm assured there is an answer, but my
calculator has plugged away at it for an hour, and not given me anything
useful.
|
rcurl
|
|
response 24 of 47:
|
Mar 28 17:05 UTC 1996 |
Do you want an analytic factoring, or a numerical answer? The latter
is easy to find for specific cases. The quartic has an interesting
structure, so I have not *given up* on factoring it. It would be easy
for specific relations between some of the constants. What is your
calculator trying to do with it?
|