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

Redeem

microchip declines

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
GMAT Instructor
Posts: 3650
Joined: Wed Jan 21, 2009 4:27 am
Location: India
Thanked: 267 times
Followed by:80 members
GMAT Score:760

microchip declines

by sanju09 » Tue May 26, 2009 5:35 am
The price of a microchip declines by 67 percent every six months. At this rate, approximately how many years will it take for the price of an $81 microchip to reach $1?
A. 1.5
B. 2
C. 3
D. 13
E. 13.5
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
Top
Source: — Problem Solving |
Legendary Member
Posts: 1035
Joined: Wed Aug 27, 2008 10:56 pm
Thanked: 104 times
Followed by:1 members

by scoobydooby » Tue May 26, 2009 6:12 am
every 6 mnths the price becomes 37/100 of the previous price.
37/100~ 36/100 ~ 9/25 ~1/3

after 1 year price: 81*(1/3)^2=9
after 2 years price: 9*(1/3)^2=1

hence, B
Top
User avatar
GMAT Instructor
Posts: 3650
Joined: Wed Jan 21, 2009 4:27 am
Location: India
Thanked: 267 times
Followed by:80 members
GMAT Score:760

by sanju09 » Tue May 26, 2009 6:25 am
I feel scoobydooby wanted to write 33/100 in place of 37/100, but cool approximation in the end.
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
Top
User avatar
GMAT Instructor
Posts: 3225
Joined: Tue Jan 08, 2008 2:40 pm
Location: Toronto
Thanked: 1710 times
Followed by:614 members
GMAT Score:800

Re: microchip declines

by Stuart@KaplanGMAT » Tue May 26, 2009 9:48 am
sanju09 wrote:The price of a microchip declines by 67 percent every six months. At this rate, approximately how many years will it take for the price of an $81 microchip to reach $1?
A. 1.5
B. 2
C. 3
D. 13
E. 13.5
Given that our number is divisible by 3, no need to approximate - quickest way will be brute force, multiplying by 1/3 each time (2/3 decrease = 1/3 of).

Start: 81
6 months: 27
1 year: 9
18 months: 3
2 years: 1

If we want to do it algebraically, the question is really asking:

If 81*(1/3)^x = 1, what's the value of x?

So, (1/3)^x = 1/81

1/(3^x) = 1/81
3^x = 81
x = 4

4*(6 months) = 2 years

Pick (b).
Image

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

Kaplan Exclusive: The Official Test Day Experience | Ready to Take a Free Practice Test? | Kaplan/Beat the GMAT Member Discount
BTG100 for $100 off a full course
Top
Post new topic Post Reply
• Page 1 of 1