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#1 2006-07-08 14:05:14

Heldensheld
Member
Registered: 2006-07-01
Posts: 25

A few.....alright maybe a lot.....of math problems here~

Here's some questions for you people to work out roflol!

Q1 If N + 2 is divisible by 3 and 2N-1 is divisble by 7. Prove that N+17 is divisible by 21. (Hint: If x is disible by 3 then x= 3a where a is an integer.)

Q2 The minute and hour hands of a clock are exactly at right angles. How long will it take for this situation to occur again.

Q3 Two spheres of diameter 6cm and 4cm touch each other at A as they rest on a horizontal table. How high is A above the table?

Q4 In a test all the questions are of equal mark value. Peter says that he answered 9 of first 10 questions and got 3/10 of the remaining questions correct. HOw many questions were set in the test if he scored 50% for the test.

That's all touched thanks again.

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#2 2006-07-08 23:56:48

Patrick
Real Member
Registered: 2006-02-24
Posts: 1,005

Re: A few.....alright maybe a lot.....of math problems here~

I would like to see what you've done so far, before helping you. This forum isn't meant for "Do my homework for me"-threads. I know that that might not be your intention, but to me it looks like it. So post what you've got, and I'm sure someone, if not me, will rush in to help you :]


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#3 2006-07-09 01:21:59

George,Y
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Registered: 2006-03-12
Posts: 1,379

Re: A few.....alright maybe a lot.....of math problems here~

He isn't delagating his homework. He's trying to challenge our IQ. big_smile

Here is my answer, Heldensheld.

1) N+17=N+2+15  3 divides N+17
2N-1=2(N+17)-35 if the N+17 is not divisible by 7, so is the right side of the equition, so is the left side. The counter and averse statement is also true that if the left side is divisible by 7, so is N+17. 7divides 2N-1, hence it also divides N+17, therefore altogether N+17 is divisible by 3*7

2) 30/(11/12)=12.72727...min

3) 2.4

4) if he get the 9 questions he answered correct definately, 30 questions


X'(y-Xβ)=0

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#4 2006-07-09 01:24:07

Patrick
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Registered: 2006-02-24
Posts: 1,005

Re: A few.....alright maybe a lot.....of math problems here~

If these are puzzles/challenges they shouldn't be in Help Me! :]


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#5 2006-07-10 02:18:35

Heldensheld
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Registered: 2006-07-01
Posts: 25

Re: A few.....alright maybe a lot.....of math problems here~

Ooooo my bad!

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#6 2006-07-10 08:41:13

Patrick
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Registered: 2006-02-24
Posts: 1,005

Re: A few.....alright maybe a lot.....of math problems here~

It's okay smile I just thought you wanted help. Don't let me scare you from posting more wink


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#7 2006-07-10 11:24:21

Ricky
Moderator
Registered: 2005-12-04
Posts: 3,791

Re: A few.....alright maybe a lot.....of math problems here~

Exactly right, Patrick.

You see, we're just like everyone else, we hate to do homework.  Especially when it's someone elses homework and for free wink.  But we absolutely love to help people out.  So when you post a question, let us know how you went about trying to solve it, even if you know it's completely off.  It lets us know that (a) you tried and (b) how you were thinking so we can help correct that thinking.  In the end, it benefits you very well.


"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

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#8 2006-07-10 11:47:44

mikau
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Registered: 2005-08-22
Posts: 1,504

Re: A few.....alright maybe a lot.....of math problems here~

I've never got these sort of problems before. What are they? Integer algebra?


A logarithm is just a misspelled algorithm.

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#9 2006-07-10 12:56:33

Ricky
Moderator
Registered: 2005-12-04
Posts: 3,791

Re: A few.....alright maybe a lot.....of math problems here~

1 is Number Theory.  2 and 3 are both Geometry.  4 is Statistics.


"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

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#10 2006-07-10 12:59:22

George,Y
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Registered: 2006-03-12
Posts: 1,379

Re: A few.....alright maybe a lot.....of math problems here~

Never mind, I'm eager to do some homework, as long as they are not so boring. Because I practiced too little and I need a bit more experience.

They are complex primary school questions, or Mathematic Olympic questions.

Heldensheld, do you know the concept of "Catching Problems" or x? Question 2 and 4 are just this type.


X'(y-Xβ)=0

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#11 2006-07-10 13:55:12

mikau
Member
Registered: 2005-08-22
Posts: 1,504

Re: A few.....alright maybe a lot.....of math problems here~

I liked those clock problems in trig.  :-)

What is number theory?


A logarithm is just a misspelled algorithm.

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#12 2006-07-10 23:14:10

Patrick
Real Member
Registered: 2006-02-24
Posts: 1,005

Re: A few.....alright maybe a lot.....of math problems here~

http://en.wikipedia.org/wiki/Number_theory smile wikipedia.org is a very good place to look for math/science related subjects. Why? Well, my guess is that a lot of people who use computers often(for other things than chatting and finding dinner recipes smile) are also the people who have an interrest in maths/science.


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#13 2006-07-11 00:58:02

heldensheld1
Guest

Re: A few.....alright maybe a lot.....of math problems here~

George,Y wrote:

Never mind, I'm eager to do some homework, as long as they are not so boring. Because I practiced too little and I need a bit more experience.

They are complex primary school questions, or Mathematic Olympic questions.

Heldensheld, do you know the concept of "Catching Problems" or x? Question 2 and 4 are just this type.

Nah, it's highschool standards.

I'm in year 10 at highschool atm.

I can sometimes get the problem straight off but sometimes I just dunno and feel like swear breaking something.

So I go the lazy option smile which won't help in exams down!

#14 2006-07-11 01:47:01

Ricky
Moderator
Registered: 2005-12-04
Posts: 3,791

Re: A few.....alright maybe a lot.....of math problems here~

Number theory is simply the study of integers and their properties.  Divisibility, primes, gcd, lcm are common topics in it.


"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

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#15 2006-07-11 16:18:29

heldensheld1
Guest

Re: A few.....alright maybe a lot.....of math problems here~

George,Y wrote:

He isn't delagating his homework. He's trying to challenge our IQ. big_smile

Here is my answer, Heldensheld.

1) N+17=N+2+15  3 divides N+17
2N-1=2(N+17)-35 if the N+17 is not divisible by 7, so is the right side of the equition, so is the left side. The counter and averse statement is also true that if the left side is divisible by 7, so is N+17. 7divides 2N-1, hence it also divides N+17, therefore altogether N+17 is divisible by 3*7

2) 30/(11/12)=12.72727...min

3) 2.4

4) if he get the 9 questions he answered correct definately, 30 questions

Thanks George but could you show me how you got the answers?

#16 2006-07-11 16:41:56

lengsamedy
Member
Registered: 2006-07-11
Posts: 2

Re: A few.....alright maybe a lot.....of math problems here~

Dear all,
Find me the advantage of Complexe number?

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#17 2006-07-11 17:53:28

Ricky
Moderator
Registered: 2005-12-04
Posts: 3,791

Re: A few.....alright maybe a lot.....of math problems here~

Just as a future note, lengsamedy, you can also start a new topic, as this question doesn't have anything to do with the topic it is in.

Complex numbers really came about when we first found that some polynomials didn't have real solutions.  x^2 = -1 being the simpilest one.  But in math, we always need a solution.  We're lost without one.  So, one was more or less invented.  But it's more than that.

Complex numbers soon became an important thing.  Out of a movement to study the real numbers properly (called Real Analysis), the same thing happened with complex numbers (called Complex Analysis).  Since then, we have used complex numbers in everything from polynomials (Abstract Algebra, specifically Galois Theory), to linear algebra with complex matrices and vectors which have much to do with physics, to differential equations.

In short, complex numbers don't have any "simple" useful applications.  The easiest one is solving polynomials.


"In the real world, this would be a problem.  But in mathematics, we can just define a place where this problem doesn't exist.  So we'll go ahead and do that now..."

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#18 2006-07-11 19:55:10

MathsIsFun
Administrator
Registered: 2005-01-21
Posts: 7,713

Re: A few.....alright maybe a lot.....of math problems here~

And very useful for Electrical Engineers working with AC (alternating current, like your normal power supply).

Apparently many years ago some guy discovered you could use complex numbers to calculate voltages etc for AC. His colleagues thought he was nuts, so he put together a circuit and said "my use of complex numbers show that if you connect a battery to this  it will blow up". They all disagreed, because it was just a simple circuit that they could see was safe. They connected a battery and ... it blew up. Mathematics won smile

I don't know the source of this story, it was told to me by an Electrical Engineering Professor.


"The physicists defer only to mathematicians, and the mathematicians defer only to God ..."  - Leon M. Lederman

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#19 2006-07-12 02:01:09

John E. Franklin
Member
Registered: 2005-08-29
Posts: 3,588

Re: A few.....alright maybe a lot.....of math problems here~

Q3 explained:
  Draw a straight line from the center of small circle (altitute 2) to center of large circle (altitude 3).
Because it is a straight line from altitude 2 to altitude 3, then the height gained to point A is exactly the same fraction of the length 5 as the 2 and 3 lengths tell you.  So 2/(2+3) is the fraction of the height difference.
The center to center of circles height difference is 3 - 2 or 1 and the fraction therefrom is 0.4 above the 2 height.
Do you want to see a picture.  I didn't scan one in yet.


igloo myrtilles fourmis

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#20 2006-07-13 02:01:53

George,Y
Member
Registered: 2006-03-12
Posts: 1,379

Re: A few.....alright maybe a lot.....of math problems here~

Franklin's answer is correct. But I guess heldensheld1 you should pick up a geometry book and check some theorems before simple calculation

for Q2, just apply relative distance and relative speed( rad) concepts. Of course you need to figure out the original speeds of two needles first.

for Q4, set the amount of remaining questions to be x.

try hard! Good luck! smile


X'(y-Xβ)=0

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#21 2006-07-14 01:20:06

heldensheld1
Guest

Re: A few.....alright maybe a lot.....of math problems here~

I HATE PETER!!!!!!!!!!!!!!

I can't get Question 4 right........so it's...

Let the amount of remaining questions be x

3x/10 +................am I too stupid?

#22 2006-07-14 02:27:48

George,Y
Member
Registered: 2006-03-12
Posts: 1,379

Re: A few.....alright maybe a lot.....of math problems here~

examine all the conditions and try to express them in mathematical way.


X'(y-Xβ)=0

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#23 2006-07-14 02:35:48

Heldensheld
Member
Registered: 2006-07-01
Posts: 25

Re: A few.....alright maybe a lot.....of math problems here~

I GOT IT, GEORGE!!!!!!!!!!!!!!!!!!!!!!!!!!!

X= Amount of total questions
Y= remaning Questions

X - Y= 10 Total Q mins remaing Q blablabla...

So 9/ X - Y + 3Y/10 = 1/2X

Times by 10(X-Y)

90 + 3Y (X-Y) =5X (X-Y)

(X-Y) cancel out.

Move 3Y...so we have

90= 5X-3Y

at the end....we have

60= 2X

and X=30!!!!!!!!!

WOOOOOT!

Sorry, George...i dunno how to get the answer with your version sad .

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#24 2006-07-14 02:45:13

Heldensheld
Member
Registered: 2006-07-01
Posts: 25

Re: A few.....alright maybe a lot.....of math problems here~

John E. Franklin wrote:

Q3 explained:
  Draw a straight line from the center of small circle (altitute 2) to center of large circle (altitude 3).
Because it is a straight line from altitude 2 to altitude 3, then the height gained to point A is exactly the same fraction of the length 5 as the 2 and 3 lengths tell you.  So 2/(2+3) is the fraction of the height difference.
The center to center of circles height difference is 3 - 2 or 1 and the fraction therefrom is 0.4 above the 2 height.
Do you want to see a picture.  I didn't scan one in yet.

I'd like that, Thanks.

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#25 2006-07-14 02:53:53

George,Y
Member
Registered: 2006-03-12
Posts: 1,379

Re: A few.....alright maybe a lot.....of math problems here~

It's okay. Glad you get it on your own! smile That's a progress!

My way is just using one variable and involves some technique. You can call it x y solution with substitution step embeded.

the amount of correct answers is
9+3/10 x
and the amount of all answers is
10+x

so
9+3x/10 = (10+x)/2
...
x=20


X'(y-Xβ)=0

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