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by Fab » Sat Nov 08, 2008 8:17 am
Q36:
If M is the least common multiple of 90, 196, and 300, which of the following is NOT a factor of M?

A. 600
B. 700
C. 900
D. 2,100
E. 4,900
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by dmateer25 » Sat Nov 08, 2008 8:46 am
First find all of the primes for the numbers:

2*3*3*5 = 90
2*2*7*7 = 196
2*2*3*5*5 = 300

The LCM will be 2*2*3*3*5*5*7*7=41000

600 = 2*2*2*3*5*5 - Not a factor because 41000 only has 2 2's as primes.

Answer is A.

You can check the others:

700 = 2*2*5*5*7 - Factor because 41000 includes all the primes

900 = 2*2*3*3*5*5 - Factor because 41000 includes all of the primes
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IMO A

by iamcste » Sat Nov 08, 2008 9:40 am
same logic as above

only one tip: Just express LCM and options in terms of powers of 2,3,5 and 7 and other primess

so that checking whether options are the factors of LCM becomes an easy task
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by Fab » Sat Nov 08, 2008 6:59 pm
The LCM will be 2*2*3*3*5*5*7*7=41000
Why? What's the rule?

THANKS.
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by logitech » Sat Nov 08, 2008 7:22 pm
Fab wrote:
The LCM will be 2*2*3*3*5*5*7*7=41000
Why? What's the rule?

THANKS.
Fab,

If you can, I would recommend you to buy Manhattan GMAT math guides. Otherwise, always keep in mind that www.google.com is your friend.

Ex: Google LCM

https://www.math.com/school/subject1/les ... 3L3GL.html

Good luck man!
LGTCH
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by raunekk » Sat Nov 08, 2008 10:28 pm
@logitech,,,

u know any faster way to solve this???
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Re: 2

by logitech » Sun Nov 09, 2008 2:38 am
Fab wrote:Q36:
If M is the least common multiple of 90, 196, and 300, which of the following is NOT a factor of M?

A. 600
B. 700
C. 900
D. 2,100
E. 4,900
All of the options are multiples of 100 = 2x2x5x5

A. 600 2x3
B. 700 7
C. 900 3x3
D. 2,100 3x7
E. 4,900 7x7

What do you guys see here ? :idea:
LGTCH
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by raunekk » Sun Nov 09, 2008 3:01 am
i m not able to get this,,,

i m gettin all options as factors of M...
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by logitech » Sun Nov 09, 2008 3:23 am
raunekk wrote:i m not able to get this,,,

i m gettin all options as factors of M...
LCM = (2^2 5^2) 3x3x7x7

So every multiple of 100 needs to be expressed with combinations of 3,3,7 and 7

A) 600 needs 2x3 but we dont have any 2 for this guy..so A is the correct answer
LGTCH
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by Fab » Sun Nov 09, 2008 11:19 am
Thanks Logitech, but my way to find the LCM is by multipliyng the common prime factors * the non common prime factors...it works...
However, I was trying to ask for a faster way..

THANKS.
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