Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

**Mathegocart****Member**- Registered: 2012-04-29
- Posts: 2,073

1.Express

as the product of 2 factors, where neither of them is 1.

2. Express as the product of 2 factors, where neither of them is 1. Do not express these 2 factors explicitly.

3. What does equal?

4. Find all integers where n! is a multiple of n^2.

5. If 3 numbers are chosen at random from first 1000 natural numbers,what is the probability that the three numbers are in G.P.? All numbers are distinct.

6. prove that is true for all non negative integers.

*Last edited by Mathegocart (2016-07-21 02:09:08)*

The integral of hope is reality.

May bobbym have a wonderful time in the pearly gates of heaven.

He will be sorely missed.

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi;

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**Mathegocart****Member**- Registered: 2012-04-29
- Posts: 2,073

bobbym wrote:

Hi;

Correct.

The integral of hope is reality.

May bobbym have a wonderful time in the pearly gates of heaven.

He will be sorely missed.

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi;

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**thickhead****Member**- Registered: 2016-04-16
- Posts: 1,086

*Last edited by thickhead (2016-07-20 04:05:57)*

**{1}Vasudhaiva Kutumakam.{The whole Universe is a family.}(2)Yatra naaryasthu poojyanthe Ramanthe tatra Devataha{Gods rejoice at those places where ladies are respected.}**

Offline

**thickhead****Member**- Registered: 2016-04-16
- Posts: 1,086

**{1}Vasudhaiva Kutumakam.{The whole Universe is a family.}(2)Yatra naaryasthu poojyanthe Ramanthe tatra Devataha{Gods rejoice at those places where ladies are respected.}**

Offline

**Mathegocart****Member**- Registered: 2012-04-29
- Posts: 2,073

thickhead wrote:

Thickhead, could you explain the process on the inequality? I used a bit of Cauchy Schwarz on this.

*Last edited by Mathegocart (2016-07-21 02:08:44)*

The integral of hope is reality.

May bobbym have a wonderful time in the pearly gates of heaven.

He will be sorely missed.

Offline

**Mathegocart****Member**- Registered: 2012-04-29
- Posts: 2,073

bobbym wrote:

Hi;

Both answers are reasonable solutions, also thickhead has a good soultion as well.

May bobbym have a wonderful time in the pearly gates of heaven.

He will be sorely missed.

Offline

**Mathegocart****Member**- Registered: 2012-04-29
- Posts: 2,073

thickhead wrote:

6 also is a solution, and 6 is not a cube. = 20

*Last edited by Mathegocart (2016-07-21 02:12:49)*

May bobbym have a wonderful time in the pearly gates of heaven.

He will be sorely missed.

Offline

**thickhead****Member**- Registered: 2016-04-16
- Posts: 1,086

Mathegocart wrote:

thickhead wrote:6 also is a solution, and 6 is not a cube. http://latex.codecogs.com/gif.latex?%5Cfrac%7B6%21%7D%7B6%5E%7B2%7D%7D = 20

I just wrote offhand. I had an obvious flash about cubes.Unless n is specified it becomes difficult to make exhaustive list.

**{1}Vasudhaiva Kutumakam.{The whole Universe is a family.}(2)Yatra naaryasthu poojyanthe Ramanthe tatra Devataha{Gods rejoice at those places where ladies are respected.}**

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi;

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**thickhead****Member**- Registered: 2016-04-16
- Posts: 1,086

bobbym is right. I had not thought properly.After knowing it it looks very simple. A composite number means at least two factors which make up for one "n" the other n being provided by the number itself. Perhaps I tried 4 and seeing it not correct went for 8 and made it a cube. Very unscientific thinking on my part.

(2)Yatra naaryasthu poojyanthe Ramanthe tatra Devataha

{Gods rejoice at those places where ladies are respected.}

Offline

**thickhead****Member**- Registered: 2016-04-16
- Posts: 1,086

*Last edited by thickhead (2016-07-24 23:20:14)*

(2)Yatra naaryasthu poojyanthe Ramanthe tatra Devataha

{Gods rejoice at those places where ladies are respected.}

Offline

**thickhead****Member**- Registered: 2016-04-16
- Posts: 1,086

*Last edited by thickhead (2016-07-25 15:28:10)*

(2)Yatra naaryasthu poojyanthe Ramanthe tatra Devataha

{Gods rejoice at those places where ladies are respected.}

Offline

**thickhead****Member**- Registered: 2016-04-16
- Posts: 1,086

Why is Mathegocart silent ?Is he too busy with other problems? One more thing instead of G.P. if the 3 numbers are in A.P. what is the probability for first 1000 natural numbers or even first n natural numbers?

(2)Yatra naaryasthu poojyanthe Ramanthe tatra Devataha

{Gods rejoice at those places where ladies are respected.}

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

Hi;

f the 3 numbers are in A.P. what is the probability for first n natural numbers?

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**thickhead****Member**- Registered: 2016-04-16
- Posts: 1,086

(2)Yatra naaryasthu poojyanthe Ramanthe tatra Devataha

{Gods rejoice at those places where ladies are respected.}

Offline

**bobbym****bumpkin**- From: Bumpkinland
- Registered: 2009-04-12
- Posts: 109,606

You are correct, further simplification is possible. Normally, I do not automatically simplify all the way. There are good reasons for this but in this case they do not apply, further simplification was called for.

**In mathematics, you don't understand things. You just get used to them.****If it ain't broke, fix it until it is.**** Always satisfy the Prime Directive of getting the right answer above all else.**

Offline

**Mathegocart****Member**- Registered: 2012-04-29
- Posts: 2,073

Could you guys explain how 1, 2, 3, 4 and 5 are done? I'm rather confused in regards with number theory.

May bobbym have a wonderful time in the pearly gates of heaven.

He will be sorely missed.

Offline

**alter ego****Member**- Registered: 2012-03-30
- Posts: 27

Hi Mathegocart,

At the time I didn't try these. I can show two now and I'll have a think about the others. No one method for all.

Q3. You'll need to know about geometric series and sum to infinity.

The series can be divided up as

5/13 + 5/13squared+ 5/13cubed + ....

+ 50/13squared + 50/13cubed + .....

+500/13cubed +.........

etc

Each line is a geometric series. I'll abbreviate each by (a,r) where a is the first term and r the common ratio.

(5/13 1/13) + (50/13squared, 1/13) + (500/13cubed 1/13) + .......

Using the sum formula we get

5/13 x 13/12 + 50/13 x 13/12 + 500/13 x 13/12 + ......

= 5/12 x 1/13 x (1 + 10/13 + 100/13squared + ......)

This last part is also a geometric (1 , 10/13) so we get

5/12 x 1/13 x 1 x 13/3 = 65/36

More follows,

Bob.

*Last edited by alter ego (2019-01-04 00:20:18)*

Offline

**alter ego****Member**- Registered: 2012-03-30
- Posts: 27

Q4.

If you divide both by n, then the question becomes when is (n-1)! divisible by n.

If n is any prime this cannot happen as none of the factorial factors can contain it because it's Prime and these are all smaller.

So what if n is not Prime? It must have a decomposition into factors all of which are smaller and so contained somewhere in the factors of the factorial. But what if such a factor occurs twice? It can be further factored using numbers we haven't yet used so n will divide the factorial.

This sounds a bit clumsy so I'll illustrate with an example.

Suppose n = 147 = 3 x 7squared

146! = 3 x 7 x 14 x other numbers so 147 divides it.

So all composite numbers have the property.

Bob

*Last edited by alter ego (2019-01-04 00:42:47)*

Offline

**Mathegocart****Member**- Registered: 2012-04-29
- Posts: 2,073

alter ego wrote:

Q4.

If you divide both by n, then the question becomes when is (n-1)! divisible by n.

If n is any prime this cannot happen as none of the factorial factors can contain it because it's Prime and these are all smaller.

So what if n is not Prime? It must have a decomposition into factors all of which are smaller and so contained somewhere in the factors of the factorial. But what if such a factor occurs twice? It can be further factored using numbers we haven't yet used so n will divide the factorial.

This sounds a bit clumsy so I'll illustrate with an example.

Suppose n = 147 = 3 x 7squared

146! = 3 x 7 x 14 x other numbers so 147 divides it.

So all composite numbers have the property.

Bob

Any idea for 5? thickhead says (sigma of stuff)/(some number choose 3), presumably that is the number of all three-number combinations, though my mind is totally lost on the numerator. Could you explain the numerator? I have to admit, I was spitballing when I saw made these problems and I didn't really have a clue on how to solve these. Bob? As in Bob Bundy?

*Last edited by Mathegocart (2019-01-04 05:19:40)*

May bobbym have a wonderful time in the pearly gates of heaven.

He will be sorely missed.

Offline

**alter ego****Member**- Registered: 2012-03-30
- Posts: 27

Hi Mathegocart

Yes, as in Bob Bundy. Someone once said that joining twice was against the rules but it isn't. I wouldn't encourage everyone to do it ... sometimes spammers who've got banned do it so it is suspicious.

If you look up my earliest posts using this name you'll find my reasoning in a problem about a professor of logic. Then, some years later I was asked whether only moderators could do a particular thing and it was helpful to have a non mod account to test it out.

Today I have a reason for using alter ego which I don't want to disclose publicly. It's to do with forum security. Please don't speculate. In a week ask again and I'll explain in a private message.

Q5 has me stumped at present. Pick any two numbers and they will be in GP. But the next term may not even be an integer so I'm stuck as to how to proceed.

I'm also not getting anywhere with Q1 and Q2 at the moment. Lots of pages of algebra but no results yet. I feel that, in both one needs to start with a binomial expansion.

Bob

Offline

**alter ego****Member**- Registered: 2012-03-30
- Posts: 27

Q1.

300^3 + 1 = 301^3 - 3x300^2 -3x300 = 301^3 -3x300(300+1)

=301^3 - 30^2 x 301

Divide by 301

301^2 - 30^2 = (301 - 30)(301 + 30) = 271 x 331

Bob

Offline