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

Redeem
TTP OnDemand GMAT Video Course
Featured Course

Target Test Prep GMAT OnDemand

Scott Woodbury-Stewart’s private virtual classroom — 400 hours of master-class video lessons for the GMAT Focus Edition.

  • 715+ score guarantee — highest in the industry (99th percentile)
  • 52 chapters · 1,500+ lessons · 4,000+ practice questions
  • 400 hours of video · 1,500+ instructor-led HD smartboard lessons
  • 300,000+ students accepted to Harvard, Stanford, Wharton, Booth & Sloan & more
  • 24/7 live support + weekly Zoom office hours with GMAT instructors
  • TTP AI Assist — 24/7 AI-powered virtual tutor for instant help
  • 1,200+ flashcards + AI-powered study assistant & daily calendar
  • OnDemand, LiveTeach & GMAT Bootcamp formats available
  • Also: GRE, SAT Math & Executive Assessment courses
  • MBA Admissions Consulting now available
  • 🏆 2025 EdTech Breakthrough Award: Test Prep Solution Provider of the Year
  • 200,000+ students served
  • 5-day free trial — $0 to start, no auto-billing, cancel anytime
★★★★★ 5.0 (559 reviews)
130-pt guarantee
$0 to start then $127/mo
Start Free 5-Day Trial Read 559 Reviews →

Percent Problem

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
User avatar
Master | Next Rank: 500 Posts
Posts: 154
Joined: Wed May 21, 2014 4:29 amFollowed by: 1 member
Thanked: 8 times
by talaangoshtari » Sun May 31, 2015 12:28 am
At the begining of the year, a certain computer problem requires 3.6 X 10^11 calculations to solve, And a computer used to solve it is capable of 1,000,000 calculations per second.At the end of the year, a new algorithm comes out which reduces the number of calculations by the factor of 10, and a new computer is buit capable of perfoming twice as many calculations per second.What percent decrease in computing time(in hrs) has been achived?

A. 60%
B. 75%
C. 85%
D. 90%
E. 95%

w2 = 9/10 w1
r2 = 2 r1

percent decrease = (t1-t2)/t1 = [(w1/r1) - (w2/r2)]/t1
= [(w1/r1) - (.9w1/2r1)]/t1 = 11/20 × 100 = 55%
Last edited by talaangoshtari on Sun May 31, 2015 1:52 am, edited 1 time in total.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members
Location: New York, NY
Thanked: 13060 times
GMAT Score:790

by GMATGuruNY » Sun May 31, 2015 1:49 am
talaangoshtari wrote:At the begining of the year, a certain computer problem requires 3.6 X 10^11 calculations to solve, And a computer used to solve it is capable of 1,000,000 calculations per second.At the end of the year, a new algorithm comes out which reduces the number of calculations by the factor of 10, and a new computer is buit capable of perfoming twice as many calculations per second.What percent decrease in computing time(in hrs) has been achived?

A. 60%
B. 75%
C. 85%
D. 90%
E. 95%
The values in red are IRRELEVANT.
Plug in EASY VALUES for the original number of calculations and the original rate.

Let the original number of calculations = 100 calculations.
Let the original rate = 1 calculation per hour.
Original time to solve the problem = w/r = 100/1 = 100 hours.

Number of calculations reduced by a factor of 10 = 100/10 = 10 calculations.
Double the rate = 2*1 = 2 calculations per hour.
New time to solve the problem = w/r = 10/2 = 5 hours.

Percent decrease from 100 hours to 5 hours = 95%.

The correct answer is E.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
Master | Next Rank: 500 Posts
Posts: 154
Joined: Wed May 21, 2014 4:29 amFollowed by: 1 member
Thanked: 8 times

by talaangoshtari » Sun May 31, 2015 2:11 am
Why w2 is equal to 1/10w1, but not 9/10w1?
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members
Location: New York, NY
Thanked: 13060 times
GMAT Score:790

by GMATGuruNY » Sun May 31, 2015 2:21 am
talaangoshtari wrote:Why w2 is equal to 1/10w1, but not 9/10w1?
To INCREASE by a factor of 10 means to MULTIPLY by 10.
To DECREASE by a factor of 10 means to DIVIDE by 10.
Thus, when w� is decreased by a factor of 10, we get:
w�/10 = (1/10)(w�).
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 518
Joined: Tue May 12, 2015 8:25 pm
Thanked: 10 times

by nikhilgmat31 » Tue Jun 02, 2015 12:18 am
At the begining of the year, a certain computer problem requires 3.6 X 10^11 calculations to solve, And a computer used to solve it is capable of 1,000,000 calculations per second.At the end of the year, a new algorithm comes out which reduces the number of calculations by the factor of 10, and a new computer is buit capable of perfoming twice as many calculations per second.What percent decrease in computing time(in hrs) has been achived?


so w2 = 9/10 of w1

also factor of 10 can be 2 or 5 or 1 or 10, Please clarify
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 363
Joined: Sun Oct 17, 2010 3:24 pmFollowed by: 3 members
Thanked: 115 times

by theCEO » Tue Jun 02, 2015 2:25 am
nikhilgmat31 wrote:At the begining of the year, a certain computer problem requires 3.6 X 10^11 calculations to solve, And a computer used to solve it is capable of 1,000,000 calculations per second.At the end of the year, a new algorithm comes out which reduces the number of calculations by the factor of 10, and a new computer is buit capable of perfoming twice as many calculations per second.What percent decrease in computing time(in hrs) has been achived?


so w2 = 9/10 of w1

also factor of 10 can be 2 or 5 or 1 or 10, Please clarify
by a factor of " is used commonly to mean the same as "multiplied by" or "divided by."
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Legendary Member
Posts: 518
Joined: Tue May 12, 2015 8:25 pm
Thanked: 10 times

by nikhilgmat31 » Tue Jun 02, 2015 2:27 am
so does reduced by factor of 10 means divided by 10
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Master | Next Rank: 500 Posts
Posts: 363
Joined: Sun Oct 17, 2010 3:24 pmFollowed by: 3 members
Thanked: 115 times

by theCEO » Tue Jun 02, 2015 2:30 am
nikhilgmat31 wrote:so does reduced by factor of 10 means divided by 10
yes it does.
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1