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#1 2006-02-28 04:13:03

Jai Ganesh
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Registered: 2005-06-28
Posts: 45,956

Number Theory

NT # 1

What is the highest power of 7 in 5000!?


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#2 2006-02-28 04:21:32

mathsyperson
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Registered: 2005-06-22
Posts: 4,900

Re: Number Theory

5000! = 5000*4999*4998*4997*...*3*2*1.

Of all the numbers up to 5000, there are 5000/7 = 714 numbers that have 7 as a factor.
Of these 714, 714/7 = 102 of them have 7² as a factor.
Of these 102, 102/7 = 14 of them have 7³ as a factor.
Of these 14, 14/7 = 2 of them have 7[sup]4[/sup] as a factor.

Adding all of these gives 832, so that is the highest power of 7 in 5000!.


Why did the vector cross the road?
It wanted to be normal.

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#3 2006-02-28 04:28:26

Jai Ganesh
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Registered: 2005-06-28
Posts: 45,956

Re: Number Theory

TE10B_B_GoodWorkApple.jpg


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#4 2006-02-28 06:02:06

krassi_holmz
Real Member
Registered: 2005-12-02
Posts: 1,905

Re: Number Theory

There's a formula:
The higest power of p(prime) that divides n! is exactly:

Last edited by krassi_holmz (2006-02-28 06:02:59)


IPBLE:  Increasing Performance By Lowering Expectations.

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#5 2006-02-28 20:18:25

Jai Ganesh
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Registered: 2005-06-28
Posts: 45,956

Re: Number Theory

NT # 2

If both 11²  and 3³  are factors of the number a * 4³ * 6² *13[sup]11[/sup], then what is the smallest possible value of a?


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#6 2006-02-28 20:23:06

krassi_holmz
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Registered: 2005-12-02
Posts: 1,905

Re: Number Theory

6^2=3^2 2^2
a=3*11^2


IPBLE:  Increasing Performance By Lowering Expectations.

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#7 2006-02-28 23:49:56

Jai Ganesh
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Registered: 2005-06-28
Posts: 45,956

Re: Number Theory

krassi_holmz, you get this award!

job-well-done.jpg


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#8 2006-03-01 00:00:53

Jai Ganesh
Administrator
Registered: 2005-06-28
Posts: 45,956

Re: Number Theory

NT # 3

A person starts multiplying consecutive positive integers from 20. How many numbers should he multiply before he will have a result that will end with 3 zeroes?


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#9 2006-03-01 02:24:09

krassi_holmz
Real Member
Registered: 2005-12-02
Posts: 1,905

Re: Number Theory

20*21*23*24*25=127512000.


IPBLE:  Increasing Performance By Lowering Expectations.

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#10 2006-03-01 03:36:47

Jai Ganesh
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Registered: 2005-06-28
Posts: 45,956

Re: Number Theory

Correct! cool


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#11 2006-03-01 20:48:23

Jai Ganesh
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Registered: 2005-06-28
Posts: 45,956

Re: Number Theory

NT # 4

What is the Least Common Multiple of 3/8, 5/36, 7/72 and 15/96?


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#12 2006-03-02 02:25:02

krassi_holmz
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Registered: 2005-12-02
Posts: 1,905

Re: Number Theory

105/4


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#13 2006-03-02 02:48:20

Jai Ganesh
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Registered: 2005-06-28
Posts: 45,956

Re: Number Theory

try.jpg


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#14 2006-03-02 03:15:37

krassi_holmz
Real Member
Registered: 2005-12-02
Posts: 1,905

Re: Number Theory

What?
105/4=3/8*70=3/8*(2*5*7)
105/4=5/36*189=5/36*(3*3*3*7)
105/4=7/72*270=7/72*(2*5*3*3*3)
105/4=15/96*168=15/96*(7*3*2*2*2)
There ISN"T a number LESS than 105/4


IPBLE:  Increasing Performance By Lowering Expectations.

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#15 2006-03-02 03:36:49

Jai Ganesh
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Registered: 2005-06-28
Posts: 45,956

Re: Number Theory

krassi_holmz,

What about 105/288?


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#16 2006-03-02 17:53:35

Jai Ganesh
Administrator
Registered: 2005-06-28
Posts: 45,956

Re: Number Theory

NT # 5

In an examination, the average marks obtained by students who passed was x%, the average marks obtained by students who failed was y% and the average marks of all the students who appeared for the examintion was z%. Find the percentage of students who failed in the examination in terms of x, y, and z.


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#17 2006-03-03 00:06:29

krassi_holmz
Real Member
Registered: 2005-12-02
Posts: 1,905

Re: Number Theory

for NT 4:
(105/288):(3/8)=(35/36), which is not an integer???


IPBLE:  Increasing Performance By Lowering Expectations.

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#18 2006-03-03 02:29:58

Jai Ganesh
Administrator
Registered: 2005-06-28
Posts: 45,956

Re: Number Theory

I concede, you are correct krassi_holmz, well done! smile


It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.

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#19 2008-06-02 05:19:13

dan howitt
Member
Registered: 2008-05-14
Posts: 21

Re: Number Theory

ganesh wrote:

Nice!


Dan Howitt

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#20 2008-07-21 14:35:10

Sudeep
Member
Registered: 2008-07-21
Posts: 20

Re: Number Theory

Want help to solve few questions...simple for people having knowledge of Euler/ Fermet theorem but i am not that great at it...

1) Two numbers 698 and 450 when divided by a certain divisor leave remainders of 9 and 8 respectively. Find the largest such divisor.

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#21 2008-07-21 14:59:00

ZHero
Real Member
Registered: 2008-06-08
Posts: 1,889

Re: Number Theory

If upon dividing 698 and 450, the divisor leaves remainders 9 and 8 respectively then it Must divide (698-9=689) and (450-8=442)!
Therefore, the required number is HCF of (689=13*53) and (442=2*13*17) which clearly is 13 !
Hence 13 is the answer...


If two or more thoughts intersect, there has to be a point!

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#22 2008-07-21 21:37:22

Sudeep
Member
Registered: 2008-07-21
Posts: 20

Re: Number Theory

What is the minimum number of identical square tiles required to completely cover a floor of dimensions 8m 70 cm by 6m 38cm

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#23 2008-07-21 23:05:43

ZHero
Real Member
Registered: 2008-06-08
Posts: 1,889

Re: Number Theory

Hi BumBumBhole!
From India haan?
Well.. Me too!
Jai Shiv Shankar!

Coming to the point..
Minimum number of squares will be needed if their size is maximum!
So required size of the squares is the square with sides of length which is HCF of 870cm & 638cm i.e. 29cm !
And number of squares is area of floor divided by area of tile..
=(870*638)/(29*29)
=330

Easy! Ain't it?

Last edited by ZHero (2008-07-21 23:30:05)


If two or more thoughts intersect, there has to be a point!

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#24 2008-07-22 00:52:38

Sudeep
Member
Registered: 2008-07-21
Posts: 20

Re: Number Theory

ok learnt the approach the HCF will be 58 and not 29 so the answer will be 870*638/58^2 = 165

thnx anyway

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#25 2008-07-22 01:00:34

Sudeep
Member
Registered: 2008-07-21
Posts: 20

Re: Number Theory

Another one ...the total number of factors of a natural number N is 45. What is the maximum number of prime numbers by which N can be divided?

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