GMAT Changed on April 16th - Read about the latest changes here

 It is currently 27 May 2018, 02:40

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# If x=-1 and n is the sum of all prime numbers less than 100,

Author Message
TAGS:

### Hide Tags

Math Revolution GMAT Instructor
Joined: 16 Aug 2015
Posts: 5452
GMAT 1: 800 Q59 V59
GPA: 3.82
If x=-1 and n is the sum of all prime numbers less than 100, [#permalink]

### Show Tags

31 Oct 2017, 01:59
Expert's post
4
This post was
BOOKMARKED
00:00

Difficulty:

15% (low)

Question Stats:

82% (01:02) correct 18% (01:39) wrong based on 71 sessions

### HideShow timer Statistics

[GMAT math practice question]

If x=-1 and n is the sum of all prime numbers less than 100, what is the value of $$x^n+x^{n+1}+x^{n+2}+x^{n+3}+x^{n+4}+x^{n+5}$$?

A. -2
B. -1
C. 0
D. 1
E. 2

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $79 for 3 month Online Course" "Free Resources-30 day online access & Diagnostic Test" "Unlimited Access to over 120 free video lessons - try it yourself" Senior Manager Joined: 17 Oct 2016 Posts: 326 Location: India Concentration: Operations, Strategy GPA: 3.73 WE: Design (Real Estate) Re: If x=-1 and n is the sum of all prime numbers less than 100, [#permalink] ### Show Tags 31 Oct 2017, 02:05 Option C When n is odd, first, third, fifth terms are odd. Hence these terms add up to -3 and the remaining terms add to +3. Hence total value is 0. When n is even the case is reverse. Again 0 Hence the value of n doesn’t matter. Posted from my mobile device _________________ Help with kudos if u found the post useful. Thanks Math Expert Joined: 02 Sep 2009 Posts: 45456 Re: If x=-1 and n is the sum of all prime numbers less than 100, [#permalink] ### Show Tags 31 Oct 2017, 02:05 MathRevolution wrote: [GMAT math practice question] If x=-1 and n is the sum of all prime numbers less than 100, what is the value of $$x^n+x^{n+1}+x^{n+2}+x^{n+3}+x^{n+4}+x^{n+5}$$? A. -2 B. -1 C. 0 D. 1 E. 2 Similar question: https://gmatclub.com/forum/if-x-1-and-n ... 32331.html _________________ Manager Joined: 09 Aug 2017 Posts: 62 Location: United States Concentration: Technology GMAT 1: 640 Q44 V33 GMAT 2: 630 Q47 V29 WE: Research (Investment Banking) Re: If x=-1 and n is the sum of all prime numbers less than 100, [#permalink] ### Show Tags 31 Oct 2017, 12:35 MathRevolution wrote: [GMAT math practice question] If x=-1 and n is the sum of all prime numbers less than 100, what is the value of $$x^n+x^{n+1}+x^{n+2}+x^{n+3}+x^{n+4}+x^{n+5}$$? A. -2 B. -1 C. 0 D. 1 E. 2 I got C, thought it took me to long at 2:58. About 90 secs in I realized that the sum of all primes under 100 is going to be even. Odd+odd...+odd+even=even. Therefore, the sequence of the exponents will be even, odd, even, odd, even, odd. So 1+-1+1+-1+1+-1=0 _________________ I'd love to hear any feedback or ways to improve my problem solving. I make a lot of silly mistakes. If you've had luck improving on stupid mistakes, I'd love to hear how you did it. Also, I appreciate any kudos. Intern Joined: 02 Sep 2015 Posts: 37 Location: India Concentration: General Management, Entrepreneurship Schools: Sauder 'Dec 18 GPA: 3.79 WE: General Management (Energy and Utilities) Re: If x=-1 and n is the sum of all prime numbers less than 100, [#permalink] ### Show Tags 01 Nov 2017, 17:03 there is no need to find whether n is even or odd. this question involves n, n+1, n+2, n+3, n+4, n+5. Either n is odd or even, we have 3 even and 3 odd. So Question reduces to 3( (-1)^e +(-1)^o ) = 3(1-1) = 0. Hence Answer is C. PS: those who want to know whether n is even or odd. As we know we have 25 prime numbers less than 100, out of which smallest prime no, is 2. So n= e+ 24*o = e+e = e. Hence, n = even Math Revolution GMAT Instructor Joined: 16 Aug 2015 Posts: 5452 GMAT 1: 800 Q59 V59 GPA: 3.82 Re: If x=-1 and n is the sum of all prime numbers less than 100, [#permalink] ### Show Tags 02 Nov 2017, 01:09 => Whatever the value of n is, $$(-1)^n+(-1)^{n+1}+(-1)^{n+2}+(-1)^{n+3}+(-1)^{n+4}+(-1)^{n+5} = 0$$, since two consecutive integer n and n+1 always have an odd integer and an even integer, and so $$(-1)^n+(-1)^{n+1}$$ = 0. Thus, the answer is C. Answer: C _________________ MathRevolution: Finish GMAT Quant Section with 10 minutes to spare The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy. "Only$79 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Re: If x=-1 and n is the sum of all prime numbers less than 100,   [#permalink] 02 Nov 2017, 01:09
Display posts from previous: Sort by