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

Redeem

Ratio / Proportion

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Source: — Problem Solving |
User avatar
Master | Next Rank: 500 Posts
Posts: 214
Joined: Mon Mar 29, 2010 1:46 pm
Location: Houston, TX
Thanked: 37 times
GMAT Score:700

by sk818020 » Sun May 09, 2010 7:27 pm
I used the following strategy

a,b,c,d are all integers increased proportionally each time thus they can be algebraically stated as;

a=x
b=x+y
c=x+2y
d=x+3y

Thus,
(a-d)/(b-c)=[x-(x+3y)]/[(x+y)-(x+2y)], simplify

(x-x-3y)/(x+y-x-2y)=-3y/-y=3

Thus, x must be at least 3 or a multiple of 3. '

Hope that helps.

Thanks,

Jared
Top
User avatar
Legendary Member
Posts: 1309
Joined: Wed Mar 17, 2010 11:41 pm
Thanked: 33 times
Followed by:5 members

by pradeepkaushal9518 » Sun May 09, 2010 9:53 pm
you can use plug in method

take 2,4,6,8 as a,b,c,d

a-d/b-c=2-8/4-6=-6/-2=3

hence option b
more 10,12,14,16

10-16/12-14=-6/-2=3 again
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 » Sun May 09, 2010 10:46 pm
r2kins wrote:If a, b, c and d are in continued proportion, then (a-d)/(b-c) >= x. What id x?
A. 2
B. 3
C. 1
D. 0
E. 4

OA - B

Pls explain.
If we solve it algebrically we would go this way...
a,b,c,d are in continued proportion
so a/b = b/c = c/d --> b=c^2/d, a = bc/d = c^3/d^2
so, (a-d)/(b-c) = {c^3/d^2 - d}/{c^2/d -c}= {c^3-d^3}/{cd(c-d)} = (c-d){c^2+cd+d^2}/cd(c-d) = {c^2+cd+d^2}/cd = c/d+1+d/c

Now since A.P >= G.P
so [c/d+1+d/c]/3>= cub. root[(c/d).1.(d/c)] =1
--> [c/d+1+d/c]>=3 --> (a-d)/(b-c) >=3.


though we can use plug in method as it would be much faster to solve that way...
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
Post new topic Post Reply
• Page 1 of 1