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

Redeem

sum of series

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Legendary Member
Posts: 1022
Joined: Mon Jul 20, 2009 11:49 pm
Location: Gandhinagar
Thanked: 41 times
Followed by:2 members

sum of series

by shashank.ism » Tue Feb 09, 2010 1:11 pm
Assume the given sum of the series, 7.5 + 15.5 + 10.5 + 13.0 + 13.5 + 10.5....+ x - y + z is
20634, (x, y, z > 0) then what is the value of the expression (2x + 3y + 5z)?


1084
1284
1464
1684
None of these
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
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 » Tue Feb 09, 2010 2:02 pm
shashank.ism wrote:Assume the given sum of the series, 7.5 + 15.5 + 10.5 + 13.0 + 13.5 + 10.5....+ x - y + z is
20634, (x, y, z > 0) then what is the value of the expression (2x + 3y + 5z)?


1084
1284
1464
1684
None of these
alternatively we find that we have 2 series.Identifying them,we can solve the question.
1st series = 7.5 + 10.5 + 13.5 + ..... +x +z = 7.5 + (7.5 + 3)+..... Hence, a =7.5,n=3
2nd series = 15.5 + 13.0 + 10.5 +.... .Hence,b=15.5 , n= -2.5
So,we can get x,y and z using the formula of sum of series till x terms = ax + n*(x-1)(x)/2
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
Post new topic Post Reply
• Page 1 of 1