Events & Promotions
|
|
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
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Apr 2610:00 AM EDT
-11:00 AM EDT
The Target Test Prep course represents a quantum leap forward in GMAT preparation, a radical reinterpretation of the way that students should study. Try before you buy with a 5-day, full-access trial of the course for FREE!
Apr 2711:00 AM EDT
-12:00 PM EDT
Prefer video-based learning? The Target Test Prep OnDemand course is a one-of-a-kind video masterclass featuring 400 hours of lecture-style teaching by Scott Woodbury-Stewart, founder of Target Test Prep and one of the most accomplished GMAT instructors
Apr 2808:00 AM PDT
-11:00 AM PDT
Whether you are just beginning your MBA journey or fine-tuning your path to a 700+ score, GMAT Day is designed to give you a competitive edge.
Smokeybear00
GMAT 1: 690 Q47 V38
Posts: 55
08 Jun 2017, 13:52
Kudos
Bookmarks
C
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
15%
(low)
Question Stats:
77% (01:12) correct
23%
(01:11)
wrong
based on 420
sessions
History
Date
Time
Result
Not Attempted Yet
If n is the sum of the first 40 positive integers, what is the greatest prime factor of n?
A. 29
B. 37
C. 41
D. 17
E. 19
A. 29
B. 37
C. 41
D. 17
E. 19
08 Jun 2017, 15:02
Kudos
Bookmarks
Smokeybear00
Nice question.
Sum of consecutive integers =
\(\frac{(First Term + Last Term)*(n)}{2}\), where n = number of terms
The first term is 1. The last term is 40.
Using the formula above, the sum is
\(\frac{(1 + 40)*(40)}{2}\)
=(41)(40) / 2
Stop there. 41 is a factor of the sum, and 41 is prime.
Answer C
Updated on: 24 Jun 2021, 10:26
Originally posted by BrentGMATPrepNow on 08 Jun 2017, 15:48.
Last edited by BrentGMATPrepNow on 24 Jun 2021, 10:26, edited 1 time in total.
Last edited by BrentGMATPrepNow on 24 Jun 2021, 10:26, edited 1 time in total.
Kudos
Bookmarks
Smokeybear00
Another useful formula: 1 + 2 + 3 + 4 + 5 + . . . .+ k = (k)(k+1)/2
So, for example, 1 + 2 + 3 + 4 + .... + 10 = (10)(10 + 1)/2 = 110/2 = 55
n = 1 + 2 + 3 + 4 + 5 + . . . .+ 40
= (40)(40 + 1)/2
= (40)(41)/2
= (20)(41)
At this point, we can see that 41 will be the greatest prime factor of n.
Answer: C
For "fun" let's finish the prime factorization of n.
We left off at: n = (20)(41)
Continue to get: n = (2)(2)(5)(41)
Cheers,
Brent
