The sum of n consecutive positive integers is 45

Oldest

Best Reply

Author

Message

TAGS:

GMAT Club team member

Joined: 02 Sep 2009

Posts: 11628

Followers: 1802

Kudos [?]: 9611 [0], given: 829

Re: Good set of DS 3 [#permalink]

26 Nov 2012, 02:40

Amateur wrote:

Bunuel wrote:

ANSWERS:
2. Is a product of three integers XYZ a prime?
(1) X=-Y
(2) Z=1

(1) x=-y --> for xyz to be a prime z must be -p AND x=-y shouldn't be zero. Not sufficient.
(2) z=1 --> Not sufficient.
(1)+(2) x=-y and z=1 --> x and y can be zero, xyz=0 not prime OR xyz is negative, so not prime. In either case we know xyz not prime.

Answer: C

i did not understand the explanation you gave..... a prime is a number which is divisible by 1 and itself right? if x,y,z are three integers..... and for it to be prime.... two for those three integers should be 1 or -1 or 1,-1.... so the third one be prime number or negative prime number....
(1) says two of them are equal in magnitude... so z can be -p to be prime or negative composite number or positive non prime in either case not sufficient...
(2) z=1 nothing said about x,y..... not sufficient

(1) + (2)
product will be a positive or negative composite number or 1..... so not a prime which is sufficient....
am i thinking correctly?

We have that x=-y and z=1, thus xyz=-x^2. Now, -x^2\leq{0}, thus it cannot be a prime number (only positive numbers are primes).

Hope it's clear.
_________________

PLEASE READ AND FOLLOW: 11 Rules for Posting!!!

RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory

COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. NEW!!!

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set. NEW!!!

What are GMAT Club Tests?
25 extra-hard Quant Tests

Find out what's new at GMAT Club - latest features and updates

Intern

Joined: 22 May 2012

Posts: 12

Concentration: Leadership, Other

GMAT Date: 12-07-2012

Followers: 0

Kudos [?]: 0 [0], given: 6

Re: The sum of n consecutive positive integers is 45 [#permalink]

06 Jan 2013, 04:24

Q Is a product of three integers XYZ a prime?
(1) X=-Y
(2) Z=1

I'm unable to understand why (1) X=-Y is not sufficient to answer the question?

In all cases if (1) X=-Y, XYZ can not be a prime number, whether X, Y being 0 or Z being negative. I may be missing out something very basic, please help.

GMAT Club team member

Joined: 02 Sep 2009

Posts: 11628

Followers: 1802

Kudos [?]: 9611 [1] , given: 829

Re: The sum of n consecutive positive integers is 45 [#permalink]

07 Jan 2013, 04:20

This post received
KUDOS

pashraddha wrote:

If x=-1, y=1, z=-7, then xyz=(-1)*1*(-7)=7=prime.

Check here: the-sum-of-n-consecutive-positive-integers-is-85413-20.html#p667155 and here: the-sum-of-n-consecutive-positive-integers-is-85413.html#p640133

Hope it helps.
_________________

Re: The sum of n consecutive positive integers is 45 [#permalink] 07 Jan 2013, 04:20

		Similar topics	Author	Replies	Last post
Similar Topics:		The sum of n consecutive positive integers starting from 1	cloaked_vessel	2	06 Mar 2005, 18:09
	2	sum of 4 consecutive positive integers	tejal777	9	28 Sep 2009, 19:40
	5	If the sum of n consecutive positive integers is 33, what of	aalriy	8	10 Dec 2010, 07:58
	8	The sum of n consecutive positive integers is 45. What is	neelesh	37	04 Apr 2008, 20:08
	3	The sum of n consecutive positive integers is 45. What is	enigma123	11	31 Jan 2012, 17:42

Main navigation

GMAT Resources

Partners

MBA Resources

GMAT ® is a registered trademark of the Graduate Management Admission Council ® (GMAC ®). GMAT Club's website has not been reviewed or endorsed by GMAC.

GMAT Courses

Admissions Consulting

The sum of n consecutive positive integers is 45

The sum of n consecutive positive integers is 45

Main navigation

GMAT Resources

Partners

MBA Resources