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

Heldensheld · 2006-07-08 14:05:14

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

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 thanks again.

Patrick · 2006-07-08 23:56:48

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 :]

George,Y · 2006-07-09 01:21:59

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

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

Patrick · 2006-07-09 01:24:07

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

Heldensheld · 2006-07-10 02:18:35

Ooooo my bad!

Patrick · 2006-07-10 08:41:13

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

Ricky · 2006-07-10 11:24:21

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 . 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.

mikau · 2006-07-10 11:47:44

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

Ricky · 2006-07-10 12:56:33

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

George,Y · 2006-07-10 12:59:22

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.

mikau · 2006-07-10 13:55:12

I liked those clock problems in trig. :-)

What is number theory?

Patrick · 2006-07-10 23:14:10

http://en.wikipedia.org/wiki/Number_theory 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 ) are also the people who have an interrest in maths/science.

heldensheld1 · 2006-07-11 00:58:02

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 and feel like breaking something.

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

Ricky · 2006-07-11 01:47:01

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

heldensheld1 · 2006-07-11 16:18:29

George,Y wrote:

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

lengsamedy · 2006-07-11 16:41:56

Dear all,
Find me the advantage of Complexe number?

Ricky · 2006-07-11 17:53:28

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.

MathsIsFun · 2006-07-11 19:55:10

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

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

John E. Franklin · 2006-07-12 02:01:09

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.

George,Y · 2006-07-13 02:01:53

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!

heldensheld1 · 2006-07-14 01:20:06

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?

George,Y · 2006-07-14 02:27:48

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

Heldensheld · 2006-07-14 02:35:48

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 .

Heldensheld · 2006-07-14 02:45:13

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.

George,Y · 2006-07-14 02:53:53

It's okay. Glad you get it on your own! 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

Math Is Fun Forum

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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