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shashank.ism
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Topic: HCF
PostTue Feb 09, 2010 1:47 pm

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Two numbers have 36 factors each and HCF of these two numbers is 36. What is the minimum possible LCM of these two numbers if the power of any prime factor in these two
numbers is not more than 3?

cube(2) X cube(3) X sqr(5) X 7
sqr(2) Xsqr( 3) X cube(5) X cube(7)
cube(2) Xcube( 3) X sqr(5) Xsqr( 7)
cube(2)X 32 X cube(5) X sqr(7)
cube(2) X sqr(3) X sqr(5) X sqr(7)

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PostSat Feb 13, 2010 3:37 pm

The numbers with HCF 36 will be

2^3 x 3^2 x 7^2; number of factors (3+1)(2+1)(2+1)=36
2^2 x 3^3 x 5^2; number of factors (2+1)(3+1)(2+1)=36

Least LCM will be 2^3 x 3^3 x 5^2 x 7^2

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PostThu Feb 18, 2010 7:00 am

Mom4MBA wrote:
The numbers with HCF 36 will be

2^3 x 3^2 x 7^2; number of factors (3+1)(2+1)(2+1)=36
2^2 x 3^3 x 5^2; number of factors (2+1)(3+1)(2+1)=36

Least LCM will be 2^3 x 3^3 x 5^2 x 7^2
Hey Mom4MBA,
I guess you quickly picked the two no.s for the HCF.But suppose instead of 36 we had gotten some bigger no.(lets say 1036)
Is there a formal step-by-step approach to get to the number of factors and the corresponding HCF??


I find that this is one of my weak area I have been ignoring for quite some time.
Can you give me a good link for HCF and LCM related properties??

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Mom4MBA
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PostThu Feb 18, 2010 8:05 am

had this question been like:
Quote:
Two numbers have 36 factors each and HCF of these two numbers is 1036. What is the minimum possible LCM of these two numbers if the power of any prime factor in these two numbers is not more than 3?
factors of 1036 = 2^2 x 7 x 37
let the two numbers be 1036 a and 1036 b
these two numbers cannot have any other new common prime factor otherwise HCF will change

Now we want each number to have 36 factors (3x3x2x2) or (4x3x3) other combinations will not be allowed as it will make the power of any prime number to go over 3.

(4x3x3) means these 2^3 x 7^2 x 37^2 ; 2^2 x 7^3 x 37^2 ; 2^2 x 7^2 x 37^3
(3x3x2x2) means one of the number can be 2^2 x 3^2 x 7 x 37 ; 2^2 x 5^2 x 7 x 37 [others will have larger values]

from the above numbers the lower two will give least LCM

So for minimum possible LCM a can be 3^2 and b can be 5^2

LCM will be 2^2 x 3^2 x 5^2 x 7 x 37

I don't know how to explain it in easier way, if anyone else can help...........

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PostThu Feb 18, 2010 8:14 am

Hey Mom4MBA,

where are you located in New Jersey? I'm from Jersey too!

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PostThu Feb 18, 2010 8:41 am

Mom4MBA wrote:
had this question been like:
Quote:
Two numbers have 36 factors each and HCF of these two numbers is 1036. What is the minimum possible LCM of these two numbers if the power of any prime factor in these two numbers is not more than 3?
factors of 1036 = 2^2 x 7 x 37
let the two numbers be 1036 a and 1036 b
these two numbers cannot have any other new common prime factor otherwise HCF will change

Now we want each number to have 36 factors (3x3x2x2) or (4x3x3) other combinations will not be allowed as it will make the power of any prime number to go over 3.

(4x3x3) means these 2^3 x 7^2 x 37^2 ; 2^2 x 7^3 x 37^2 ; 2^2 x 7^2 x 37^3
(3x3x2x2) means one of the number can be 2^2 x 3^2 x 7 x 37 ; 2^2 x 5^2 x 7 x 37 [others will have larger values]

from the above numbers the lower two will give least LCM

So for minimum possible LCM a can be 3^2 and b can be 5^2

LCM will be 2^2 x 3^2 x 5^2 x 7 x 37

I don't know how to explain it in easier way, if anyone else can help
...........
Hey Mom4MBA,
Thanks for the explanation u had given above.Its easily understandable and maybe in the most easiest way.
I guess the imp. properties we have to take note of are:-

Quote:
these two numbers cannot have any other new common prime factor otherwise HCF will change

36 factors (3x3x2x2) or (4x3x3) other combinations will not be allowed as it will make the power of any prime number to go over 3.

from the above numbers the lower two will give least LCM
I thought that since 36 was a small no., you easily got to its factors.[For a small no.,we can easily use hit-and-trial]
But for large no.s hit-and-trial would have become very cumbersome.

Anyways,thanks again for the formal method. Smile

Do you have any guide for learning the LCM and HCF properties??Any gud link would do.
On google search,I get wikipedia[http://en.wikipedia.org/wiki/Greatest_common_divisor]but lots of irrelevant information is also listed there and it gets kind of tiring going through the whole thing.
I need to brush up on the above properties so ur help would be appreciated.

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PostThu Feb 18, 2010 10:05 am

Good that you understood because I am no expert at explaining or finding a shorter approach. I just got started with my preparation. Actually I have few Career Launcher booklets and also Math book by HC Verma (not that good a book but some fundas are good), while coming to US what ever I could get hold of I packed. Sorry no good link that I know of.
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PostThu Feb 18, 2010 10:23 am

Mom4MBA wrote:
Good that you understood because I am no expert at explaining or finding a shorter approach. I just got started with my preparation. Actually I have few Career Launcher booklets and also Math book by HC Verma (not that good a book but some fundas are good), while coming to US what ever I could get hold of I packed. Sorry no good link that I know of.
Hey thats fine. You have written that you have CL booklets (Have u already given the MBA entrance exams??)
Also,HC Verma is a physics book,no??
I read it while prep 4 engg entrance exams.
Has he also authored any maths book???
So,I guess you are working in the US..

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PostThu Feb 18, 2010 10:28 am

harsh.champ wrote:
Mom4MBA wrote:
Good that you understood because I am no expert at explaining or finding a shorter approach. I just got started with my preparation. Actually I have few Career Launcher booklets and also Math book by HC Verma (not that good a book but some fundas are good), while coming to US what ever I could get hold of I packed. Sorry no good link that I know of.
Hey thats fine. You have written that you have CL booklets (Have u already given the MBA entrance exams??)
Also,HC Verma is a physics book,no??
I read it while prep 4 engg entrance exams.
Has he also authored any maths book???
So,I guess you are working in the US..
See Here..who is this?? they have started a" self proclaimed....happy pep talk among themselves...!!

A novel in the process??? Huh??

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PostThu Feb 18, 2010 10:34 am

shashank.ism wrote:
Two numbers have 36 factors each and HCF of these two numbers is 36. What is the minimum possible LCM of these two numbers if the power of any prime factor in these two
numbers is not more than 3?

cube(2) X cube(3) X sqr(5) X 7
sqr(2) Xsqr( 3) X cube(5) X cube(7)
cube(2) Xcube( 3) X sqr(5) Xsqr( 7)
cube(2)X 32 X cube(5) X sqr(7)
cube(2) X sqr(3) X sqr(5) X sqr(7)
Shashank,

Plz man..we beg u...y dont u post the questions properly?? Do u really feel people have that much patience in "deciphering" the codes u used??

Already we are here we want to get some knoweldge..But seeing all your posts..u never know man How many souls are"cursing" you for the trouble u cause..This is truth man..Plz dont take wrath of others( that too this way Buddy!)

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Mom4MBA
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PostThu Feb 18, 2010 10:35 am

I am so sorry, that was RS Agarwal not HC Verma (ah, I still remember this book!)
My brother was preparing for CAT so I got few of his books, but the pattern and syllabus of CAT and GMAT are very different. I am not not working.

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