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

Redeem

plzzzz help out....

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Problem Solving |
User avatar
Legendary Member
Posts: 1132
Joined: Mon Jul 20, 2009 3:38 am
Location: India
Thanked: 64 times
Followed by:6 members
GMAT Score:760

by harsh.champ » Fri Feb 19, 2010 12:13 pm
jagdeep wrote:If the sum of the consecutive integers from -35 to n inclusive is 150, what is the value of n?

A)
36

B)
39

C)
40

D)
60

E)
185
All the options choice are +ve so we can assume that n is +ve.

First of all we have to calculate the sum from -35 to 0.
Then,we can calculate the sum from 0 to n.

For negative sum,we get -[35 + 34 + 33 +......+ 3 + 2 + 1]
=-[(35)(35 + 1)]/2 = -630

For positive sum we have n(n+1)/2 =x.
Now,x -630 = 150
Hence,x=780
or n(n+1)/2 =780
=>n(n+1) = 1560 =39 x 40
Hence n=39 which is B.
Last edited by harsh.champ on Fri Feb 19, 2010 12:19 pm, edited 1 time in total.
It takes time and effort to explain, so if my comment helped you please press Thanks button :)



Just because something is hard doesn't mean you shouldn't try,it means you should just try harder.

"Keep Walking" - Johnny Walker :P
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 117
Joined: Wed Dec 30, 2009 1:57 pm
Location: India
Thanked: 4 times
Followed by:1 members

by abhi332 » Fri Feb 19, 2010 12:16 pm
If the sum of the consecutive integers from -35 to n inclusive is 150, what is the value of n?

A)
36

B)
39

C)
40

D)
60

E)
185

-35 to -1 will have 35 terms

0 ..... middle of -35 to +35

+35 to +1 will have 35 terms


also when we add above 2 sequence we get 0

-35 to +35 will contribute 0 sum and numbers of terms in sequence are 71 (-35 + -34 +.....-1+ 0 + 1+........34+35)

only choice E is above 71

IMO E is the ans
Last edited by abhi332 on Fri Feb 19, 2010 12:27 pm, edited 1 time in total.
Top
User avatar
Legendary Member
Posts: 1132
Joined: Mon Jul 20, 2009 3:38 am
Location: India
Thanked: 64 times
Followed by:6 members
GMAT Score:760

by harsh.champ » Fri Feb 19, 2010 12:24 pm
abhi332 wrote:
If the sum of the consecutive integers from -35 to n inclusive is 150, what is the value of n?

A)
36

B)
39

C)
40

D)
60

E)
185

-35 to -1 will have 35 numbers

0 ..... middle of -35 to +35

+35 to +1 will have 35 numbers


also when we add above 2 sequence we get 0

-35 to +35 will contribute 0 sum and numbers in sequence are 71 (-35 + -34 +.....-1+ 0 + 1+........34+35)

only choice E is above 71

IMO E is the ans
The answer would be B.
I think you made a mistake in understanding the problem.
numbers in sequence are 71 (-35 + -34 +.....-1+ 0 + 1+........34+35)
You have calculated the numbers in the sequence which sure is greater than 71(Actually it is 75(71+4) when n=39)
But in the question we are asked the value of n(which is a +ve integer)
It takes time and effort to explain, so if my comment helped you please press Thanks button :)



Just because something is hard doesn't mean you shouldn't try,it means you should just try harder.

"Keep Walking" - Johnny Walker :P
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 117
Joined: Wed Dec 30, 2009 1:57 pm
Location: India
Thanked: 4 times
Followed by:1 members

by abhi332 » Fri Feb 19, 2010 12:32 pm
Hello Harsh,

Thanks, I made a mistake writing terms as numbers, I have corrected that in the post.

Also, I have actually found the number of terms in original solution.

Can you tell me what I am missing
Top
User avatar
Legendary Member
Posts: 1132
Joined: Mon Jul 20, 2009 3:38 am
Location: India
Thanked: 64 times
Followed by:6 members
GMAT Score:760

by harsh.champ » Fri Feb 19, 2010 12:37 pm
abhi332 wrote:Hello Harsh,

Thanks, I made a mistake writing terms as numbers, I have corrected that in the post.

Also, I have actually found the number of terms.

Can you tell me what I am missing
Just note that sum of 36+37+38+39 = 150 which is the sum in the question.
Hence,the last term =n=39 which is the answer.
It takes time and effort to explain, so if my comment helped you please press Thanks button :)



Just because something is hard doesn't mean you shouldn't try,it means you should just try harder.

"Keep Walking" - Johnny Walker :P
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 117
Joined: Wed Dec 30, 2009 1:57 pm
Location: India
Thanked: 4 times
Followed by:1 members

by abhi332 » Fri Feb 19, 2010 12:39 pm
Hey Harsh, Thank for your explanation,

I got my mistake :)
Top
Junior | Next Rank: 30 Posts
Posts: 20
Joined: Fri Nov 13, 2009 3:42 pm
Thanked: 1 times

by jagdeep » Fri Feb 19, 2010 12:57 pm
thanks guys....

Answer is B
Top
User avatar
Legendary Member
Posts: 1022
Joined: Mon Jul 20, 2009 11:49 pm
Location: Gandhinagar
Thanked: 41 times
Followed by:2 members

by shashank.ism » Sat Feb 20, 2010 7:50 am
jagdeep wrote:If the sum of the consecutive integers from -35 to n inclusive is 150, what is the value of n?

A) 36
B) 39
C) 40
D) 60
E) 185
Since -35 to 35 willl give the value = 0 and less than that will give value as -ve

so we have to check for values above 35
since 150 is a very small sum we can check it by addition also
36+37+38+39 = 150 (I applied this for fast calculation, hence this problem could be solved in 4 sec)
so Ans B
If there is a bigger no. we will go by AP process..
My Websites:
www.mba.webmaggu.com - India's social Network for MBA Aspirants

www.deal.webmaggu.com -India's online discount, coupon, free stuff informer.

www.dictionary.webmaggu.com - A compact free online dictionary with images.

Nothing is Impossible, even Impossible says I'm possible.
Top
User avatar
Legendary Member
Posts: 1560
Joined: Tue Nov 17, 2009 2:38 am
Thanked: 137 times
Followed by:5 members

by thephoenix » Sat Feb 20, 2010 8:17 am
jagdeep wrote:If the sum of the consecutive integers from -35 to n inclusive is 150, what is the value of n?

A)
36

B)
39

C)
40

D)
60

E)
185
clue1: 1st term=-35
clue2:no's r consecutive
implied clue summation of -35 to 35 will be 0 as all terms get cancel out
now summation of 36 to n is 150
now 36*5=180 >150
----> there can be only 4 no's
36+37+38+29=150 HENCE LAST TERM IS 39
Top
Post new topic Post Reply
• Page 1 of 1