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HCF

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Source: — Data Sufficiency |
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by Frankenstein » Sun Jun 12, 2011 6:01 am
Hi,
From(1) :
if a=3, b=6...HCF is 3
if a=6, b=12..HCF is 6
Insufficient

From(2):
if a=2,b=5 then HCF is 1
if a=3,b=6 then HCF is 3
Insufficient

Both(1)&(2):
a and b are 3n and 3(n+1) in any order.
As n and (n+1) are co-primes..i.e. HCF is 1, HCF of 3n and3(n+1) is 3*1 = 3
Sufficient

Hence, C
Cheers!

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by Anurag@Gurome » Sun Jun 12, 2011 7:04 am
vinayreguri wrote:What is HCF of a & b
1. 3 is a factor of a & b
2. The difference between a & b is 3


Statement 1: There may be some common factor of a and b which is greater than 3.

Not sufficient

Statement 2: If a = 1 and b = 4 --> HCF = 1
If a = 3 and b = 6 --> HCF = 3

Not sufficient

1 & 2 Together: Say, a = 3n then b = (3n + 3) = 3(n + 1)
As n and (n + 1) has no common factor other than 1, common factors of a and b are 1 and 3. Hence HCF of a and b is 3.

Sufficient

The correct answer is C.
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