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factorization

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Source: — Data Sufficiency |
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by pepeprepa » Sat Jul 26, 2008 12:52 am
C for me
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Re: factorization

by Ian Stewart » Sat Jul 26, 2008 3:13 am
Mani_mba wrote:If n and k are positive integers, is n divisible by 6?
(1) n = k(k + 1)(k - 1)
(2) k – 1 is a multiple of 3.
A. From 1), n is the product of three consecutive integers: k-1, k and k+1. So n is divisible by 3! = 6. (the product of d consecutive integers is always divisible by d!). Statement 2) is clearly insufficient on its own.
For online GMAT math tutoring, or to buy my higher-level Quant books and problem sets, contact me at ianstewartgmat at gmail.com

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by Mani_mba » Sat Jul 26, 2008 3:30 am
Thanks Ian !
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by Bidisha800 » Mon Feb 09, 2009 12:47 am
I understand why stmt 1 is sufficient but do not understand how stmt 2 is NOT sufficient.

Probably I'm missing something so please help me out...

k-1 = 3m
k=3m+1
k+1 =3m+2

n=k(k+1)(k-1)
=3m(3m+1)(3m+2)

m=0 n=0 divisible by 6
m=1 n=3.4.5 divisible by 6
m=2 n=6.7.8 divisible by 6
m=3 n=9.10.11 divisible by 6
.....

so why (B) is CLEARLY insufficient by its own ?


so why the answer is (A) ?
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by Vemuri » Mon Feb 09, 2009 1:00 am
Bidisha800 wrote:I understand why stmt 1 is sufficient but do not understand how stmt 2 is NOT sufficient.

Probably I'm missing something so please help me out...

k-1 = 3m
k=3m+1
k+1 =3m+2

n=k(k+1)(k-1)
=3m(3m+1)(3m+2)

m=0 n=0 divisible by 6
m=1 n=3.4.5 divisible by 6
m=2 n=6.7.8 divisible by 6
m=3 n=9.10.11 divisible by 6
.....

so why (B) is CLEARLY insufficient by its own ?


so why the answer is (A) ?
You mixed the 1st statement with the 2nd. You should consider the 2nd statement seperately inorder to determine if it is sufficient or not. So, with that

k-1 = 3m
k=3m+1
k+1 =3m+2

is not enough to answer the question if n is divisible by 6 or not.
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by Bidisha800 » Mon Feb 09, 2009 1:02 am
Vemuri wrote:
Bidisha800 wrote:I understand why stmt 1 is sufficient but do not understand how stmt 2 is NOT sufficient.

Probably I'm missing something so please help me out...

k-1 = 3m
k=3m+1
k+1 =3m+2

n=k(k+1)(k-1)
=3m(3m+1)(3m+2)

m=0 n=0 divisible by 6
m=1 n=3.4.5 divisible by 6
m=2 n=6.7.8 divisible by 6
m=3 n=9.10.11 divisible by 6
.....

so why (B) is CLEARLY insufficient by its own ?


so why the answer is (A) ?
You mixed the 1st statement with the 2nd. You should consider the 2nd statement seperately inorder to determine if it is sufficient or not. So, with that

k-1 = 3m
k=3m+1
k+1 =3m+2

is not enough to answer the question if n is divisible by 6 or not.
THANKS ....

STUPID ME ... IT IS 3:45 AM .... I'M SLEEPY
Drill baby drill !

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