Register    Login    Search    Rss Feeds

 Page 1 of 1 [ 4 posts ] 



 
Author Message
 Post subject: The sum of first 50 even numbers is 2550 .What is the sum of
 Post Posted: Mon Jan 18, 2010 4:18 pm 
Offline
Students


Posts: 24
pLease correct me if I'm wrong:

Please correct if i m wrong:


Sum=average*numbers of terms

Numbers of term=(200-102)/2 =43

Average= (FIRST +LAST)/2 = (200+102)/2 = 151

SUM = 151*43 = 6493


Top 
 Post subject: Re: The sum of first 50 even numbers is 2550 .What is the sum of
 Post Posted: Wed Jan 20, 2010 2:51 pm 
Offline
ManhattanGMAT Staff


Posts: 898
Location: St. Louis, MO
Please post the full text of the question. Is it "what is the sum of the next 50 even numbers?" And what are the choices?

imanemekouar wrote:
Sum=average*numbers of terms

Numbers of term=(200-102)/2 =43

Your error is here. The number of even numbers between 102 and 200, inclusive, is
(200-102)/2 + 1 = 98/2 + 1 = 49 + 1 = 50.

{You divide the range by 2 since only half of any set of consecutives is even, and "add one before your done" to include 102 as one of the terms you are counting.}

Also, think about this: There are 50 positive even numbers up to and including 100 (i.e. 2, 4, 6, ...., 98, 100). The set from 102 to 200 is just the first set shifted up by 100.

Thus, Sum = Average * Number of Terms = 151 * 50 = 7550. Check it another way: if each term is 100 more than the corresponding term in the 2 to 100 set, and there are 50 terms, this sum should be 5000 greater than the 2550 sum given.

_________________
Emily Sledge
Instructor
ManhattanGMAT


Top 
 Post subject: Re: The sum of first 50 even numbers is 2550 .What is the sum of
 Post Posted: Sun Sep 30, 2012 7:23 am 
Offline
Forum Guests


Posts: 1
Hi,

Sorry to open this topic again.

Full question is here.

1. The sum of first 50 even numbers is 2550. What is the sum of even numbers from 102 to 200 inclusive?
A. 5100
B. 7550
C.10100
D.15500
E. 20100

I reached the answer to this question as described below.

Sum of first n even natural numbers = n(n + 1)

so the first 50 integer's sum = 50(51) = 2550 as given in the question stem.

Sum of first 100 integer (2550 covers integers till 100, and 102 and 200 are inclusive) = 100(101) = 10100

Sum of integers from 102 to 200 therefore = 10100-2550 = 7550.

Can someone confirm if my approach is correct?


Top 
 Post subject: Re: The sum of first 50 even numbers is 2550 .What is the sum of
 Post Posted: Mon Oct 01, 2012 4:53 am 
Offline
ManhattanGMAT Staff


Posts: 11197
here's a thread with approximately a million posts on this problem:

sum-of-first-50-even-numbers-is-t4166.html

if you have any more questions after reading that thread, post them over there, not here. this thread is now locked, so that we don't have tons of different threads on the same problem.

_________________
Pueden hacerle preguntas a Ron en castellano
Potete chiedere domande a Ron in italiano
On peut poser des questions à Ron en français
Voit esittää kysymyksiä Ron:lle myös suomeksi

Un bon vêtement, c'est un passeport pour le bonheur.
Yves Saint-Laurent


Top 
Display posts from previous:  Sort by  
 
 Page 1 of 1 [ 4 posts ] 





Who is online

Users browsing this forum: No registered users and 0 guests

 
 

 
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to: