BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Possible errors in Number Property Guide for odd/even(s)

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Newbie | Next Rank: 10 Posts
Posts: 2
Joined: Fri Feb 08, 2013 5:32 pm

Possible errors in Number Property Guide for odd/even(s)

by murphydb711 » Fri Apr 12, 2013 10:26 am
Hello,

I could use some help. I've been working on number properties today in the guidebook I purchased specifically for NPs. I admit that NPs are a very large weakness for me, so the errors are probably on met, but I've gone over the following three problems several times using DS strategies and my answers don't match the guidebook. I went to the errata website and no errors were listed for the odd/even CHPT. Finding three unlisted errors in one CHPT has got to be me, but I'd like to see what the rest of the forum comes up with their own answers to see if it matches mine or the book. Thanks for your help.

1. If x>1, what is the value of x?

1) There are x unique factors of x.
2) The sum of x and any prime number larger than x is odd.

2. What is the remainder when a is divided by 4?

1) a is the square of an odd integer.
2) a is a multiple of 3.

3. This is not a DS question, instead you were to answer if x is odd, even, or can't be determined & ALL VARIABLES ARE INTEGERS -
- If x/y yields an odd integer, what is x?
Top
Source: — Data Sufficiency |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 511
Joined: Wed Aug 11, 2010 9:47 am
Location: Delhi, India
Thanked: 344 times
Followed by:86 members

by Anju@Gurome » Fri Apr 12, 2013 10:41 am
murphydb711 wrote:1. If x > 1, what is the value of x?

1) There are x unique factors of x.
2) The sum of x and any prime number larger than x is odd.
Minimum possible value of x is 2.

Statement 1: For x to have x unique factors, x must be divisible by all the integers starting from 1 to x. But for any x greater than 2, x and (x - 1) will be coprime integers. Hence, for any x > 2, it is not possible that (x - 1) will be a factor of x. Only possible value of x is 2.

Sufficient

Statement 2: (x + p) is odd, where p is a prime number such that p > 2
All prime numbers greater than p are odd. Hence, x must be even.

Now x can have any even value. For example,
  • x = 2, p = 5
    x = 4, p = 5
Not sufficient

The correct answer is A.
Anju Agarwal
Quant Expert, Gurome

Backup Methods : General guide on plugging, estimation etc.
Wavy Curve Method : Solving complex inequalities in a matter of seconds.

§ GMAT with Gurome § Admissions with Gurome § Career Advising with Gurome §
Top
Master | Next Rank: 500 Posts
Posts: 423
Joined: Fri Jun 11, 2010 7:59 am
Location: Seattle, WA
Thanked: 86 times
Followed by:2 members

by srcc25anu » Fri Apr 12, 2013 10:42 am
Q1. x > 1 (given)
what is x?

ST1: there are x unique factors of x
lets try a few values for x
if x = 2 (as x>1), factors = 1,2 (satisfies)
if x=3, factors= 1,3 (DOES NOT SATISFY as there are only 2 unique factors of X and X = 2)
x = 4, factors= 1,2,4 (DOES NOT SATISFY as there are 3 unique factors of X and x = 4)
There is no numbers besides 2 that will satisfy this.

hence St1 is sufficient.

St2: sum of x and any prime larger than x = odd
Odd = odd + Even or Odd = Even + odd
if x = 2, prime no = 3 sum = odd
but if x = 3, prime no = 5 (odd) then sum = even (odd + odd = even)
not sufficient

Hence IMO it should be A
Top
Master | Next Rank: 500 Posts
Posts: 423
Joined: Fri Jun 11, 2010 7:59 am
Location: Seattle, WA
Thanked: 86 times
Followed by:2 members

by srcc25anu » Fri Apr 12, 2013 10:45 am
Q2. remainder when a / 4 ?

ST1: a = sq of an odd integer
if a = 1, a^2 = 1 and 1/4 = rem 1
if a = 3, a^2 = 9 and 9/4 = rem 1
if a = 5, a^2 = 25 and 25/4 = rem 1

Sufficient

ST2: a = multiple of 3
if a = 3, 3/4 = rem 3
if a = 6, 6/4 = rem 2
Not Sufficient

Hence Ans A
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 511
Joined: Wed Aug 11, 2010 9:47 am
Location: Delhi, India
Thanked: 344 times
Followed by:86 members

by Anju@Gurome » Fri Apr 12, 2013 10:46 am
murphydb711 wrote:2. What is the remainder when a is divided by 4?

1) a is the square of an odd integer.
2) a is a multiple of 3.
Statement 1: Let us assume a = (2n + 1)², where n is some non-negative integer.
So, a = (4n² + 4n + 1) = 4*(n² + n) + 1 = (some multiple of 4) + 1
Hence, when a is divided by 4, the remainder is 1.

Sufficient

Statement 2: Consider the following two examples,
a = 0 ---> remainder is 0
a = 3 ---> remainder is 3

Not sufficient

The correct answer is A.
Anju Agarwal
Quant Expert, Gurome

Backup Methods : General guide on plugging, estimation etc.
Wavy Curve Method : Solving complex inequalities in a matter of seconds.

§ GMAT with Gurome § Admissions with Gurome § Career Advising with Gurome §
Top
Master | Next Rank: 500 Posts
Posts: 423
Joined: Fri Jun 11, 2010 7:59 am
Location: Seattle, WA
Thanked: 86 times
Followed by:2 members

by srcc25anu » Fri Apr 12, 2013 10:47 am
Q3. if x/y = odd integer, it could either be 9/3 = 3 (where x = odd) or 6/2 = 3 (where x = even)
only with the above information, with no information about y, we cannot for certain say anything about x
Top

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 511
Joined: Wed Aug 11, 2010 9:47 am
Location: Delhi, India
Thanked: 344 times
Followed by:86 members

by Anju@Gurome » Fri Apr 12, 2013 10:48 am
murphydb711 wrote:3. This is not a DS question, instead you were to answer if x is odd, even, or can't be determined & ALL VARIABLES ARE INTEGERS -
- If x/y yields an odd integer, what is x?
Consider the following examples,
x = 1, y = 1 ---> x odd
x = 2, y = 2 ---> x even

Hence, can't be determined.
Anju Agarwal
Quant Expert, Gurome

Backup Methods : General guide on plugging, estimation etc.
Wavy Curve Method : Solving complex inequalities in a matter of seconds.

§ GMAT with Gurome § Admissions with Gurome § Career Advising with Gurome §
Top
Post new topic Post Reply
• Page 1 of 1