Gold depreciated

Expert replies

sanju09: GMAT Instructor; Posts: 3650; Joined: Wed Jan 21, 2009 4:27 amFollowed by: 80 members; Location: India; Thanked: 267 times; GMAT Score:760

by sanju09 » Mon Mar 30, 2009 6:01 am

Gold depreciated at a rate of x% per year between 2000 and 2005. If 1 lb of gold cost S dollars in 2001 and T dollars in 2003, how much did it cost in 2002?

A. T S/2
B. T sqrt (T/S)
C. T sqrt (S)
D. T S/sqrt (T)
E. sqrt (S T)

OA E

The mind is everything. What you think you become. -Lord Buddha

Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001

www.manyagroup.com

Like this post

Source: Beat The GMAT — Problem Solving | Mon Mar 30, 2009 6:01 am

moutar: Senior | Next Rank: 100 Posts; Posts: 92; Joined: Wed Mar 25, 2009 12:13 pm; Thanked: 10 times

by moutar » Mon Mar 30, 2009 6:21 am

At the end of 2002 gold costs (100 - x)*S/100

At the end of 2003 gold costs:

((100 - x)/100)^2 * S = T

100^2*T/S = (100 - x)^2

100*sqrt(T/S) = 100 - x

x = 100 - 100*sqrt(T/S)

In 2002:

Cost = (100 - (100 - 100*sqrt(T/S)))*S/100
= (100*sqrt(T/S))S/100
= S*sqrt(T/S)
= sqrt (S*T) = Answer E

Thats not nice. I'm sure theres a better and quicker way but that does get you the answer.

Like this post

scoobydooby: Legendary Member; Posts: 1035; Joined: Wed Aug 27, 2008 10:56 pmFollowed by: 1 member; Thanked: 104 times

by scoobydooby » Mon Mar 30, 2009 6:36 am

let the cost of gold be 100 in 2000. let it decrease by 50% every year

2001: 100*1/2=50........S
2002: 50*1/2=25
2003: 25*1/2=12.50......T

substituting values of S and T in the answer choices, the one that gives the value of 25 will be the answer.

C. T sqrt (S) =12.50*(50)^1/2 >25

D. T S/sqrt (T) =(100/2 *25/2)/(25/2)^1/2=125 *2^1/2 >25

E . sqrt (S T)= (50*25/2)^1/2 =25

hence E

Like this post

sacx: Master | Next Rank: 500 Posts; Posts: 139; Joined: Wed Oct 22, 2008 4:36 am; Thanked: 17 times

by sacx » Mon Mar 30, 2009 6:51 am

It is easier to pick up number and solve it

Let the cost of 1 lb of gold in year 2000 was 1000 and it depreciated 10 % annually

therefore, cost in 2001 = 900 (or S)
cost in 2002 = 810 ( the unkown)
cost in 2003 = 729 (or T)

A. T S/2 = 729*450 (this would be much greater than 810)
B. T sqrt (T/S) = 729 * sqrt(729/900) = 729 * 0.9 (less than 810)
C. T sqrt (S) = 729 * sqrt (900) = 729 *30 (much greater than 810)
D. T S/sqrt (T) = sqrt (T) * S = 81 * 900 ( much greater than 810)
E. sqrt (S T) = sqrt (729 * 900) = 27*30 = 810 Bingo!!

With these type of questions its always better to start with option E, and then try C

SACX

Like this post

cubicle_bound_misfit: Master | Next Rank: 500 Posts; Posts: 246; Joined: Mon May 19, 2008 7:34 am; Location: Texaco Gas Station; Thanked: 7 times

by cubicle_bound_misfit » Mon Mar 30, 2009 7:10 am

I have a question.

For this type of Q , how to understand picking which no will be ideal?

Cubicle Bound Misfit

Like this post

bluementor: Master | Next Rank: 500 Posts; Posts: 418; Joined: Wed Jun 11, 2008 5:29 am; Thanked: 65 times

by bluementor » Mon Mar 30, 2009 7:58 am

S ---> M ---> T where M is the price in 2002

depreciation is x% per year.

Therefore:

M = S*(100-x)/x
T = M*(100-x)/x

Lets say (100 - x)/x = y (I am doing this simplification because the answer choices are not in x)

So,

M = Sy and T=My

M = S*(T/M)
M^2 = ST
M = sqrt(ST) Choose E

-BM-

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review