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 →

fractions

Expert replies
Post new topic Post Reply
Previous Topic Next Topic
Senior | Next Rank: 100 Posts
Posts: 72
Joined: Tue Nov 05, 2013 4:35 pmFollowed by: 4 members
by Ankitaverma » Wed Dec 04, 2013 10:28 am
If 1/2 of the air in a tank is removed with each stroke of a vacuum pump, what fraction of the original amount of air has been removed after 4 strokes?
(A) 15/16
(B) 7/8
(C) 1/4
(D) 1/8
(E) 1/16
Q/A-a
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Source: — Problem Solving |

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 16207
Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members
Location: Vancouver, BC
Thanked: 5254 times
GMAT Score:770

by Brent@GMATPrepNow » Wed Dec 04, 2013 10:35 am
Ankitaverma wrote:If 1/2 of the air in a tank is removed with each stroke of a vacuum pump, what fraction of the original amount of air has been removed after 4 strokes?
(A) 15/16
(B) 7/8
(C) 1/4
(D) 1/8
(E) 1/16
Q/A-a
Start: All of the air is in the tank
After 1st stroke: 1/2 of the air REMAINS in tank
After 2nd stroke: 1/4 of the air REMAINS in tank
After 3rd stroke: 1/8 of the air REMAINS in tank
After 4th stroke: 1/16 of the air REMAINS in tank

We want to determine the fraction of air that has been REMOVED
So, if 1/16 of the air REMAINS in the tank, we know that [spoiler]15/16[/spoiler] has been REMOVED

Answer: A

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
Image
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 » Wed Dec 04, 2013 12:25 pm
Ankitaverma wrote:If 1/2 of the air in a tank is removed with each stroke of a vacuum pump, what fraction of the original amount of air has been removed after 4 strokes?
(A) 15/16
(B) 7/8
(C) 1/4
(D) 1/8
(E) 1/16
Q/A-a
The amount of air is reduced by 1/2 four times.
Plug in a value that can be divided by 2 four times.
Let the original amount of air = 2� = 16 units.

After 1 stroke, the remaining amount of air = 8 units.
After 2 strokes, the remaining amount of air = 4 units.
After 3 strokes, the remaining amount of air = 2 units.
After 4 strokes, the remaining amount of air = 1 unit.
.
Since only 1 unit remains, the amount removed = 15 units.
(amount removed)/(original amount) = 15/16.

The correct answer is A.
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

GMAT/MBA Expert

User avatar
Elite Legendary Member
Posts: 10392
Joined: Sun Jun 23, 2013 6:38 pmFollowed by: 511 members
Location: Palo Alto, CA
Thanked: 2867 times
GMAT Score:800

by [email protected] » Wed Dec 04, 2013 2:16 pm
Hi Ankitaverma,

Both Brent and Mitch provide logical solutions to this problem. Here's another way to look at it:

Since we don't know how much air we're starting with, the tank could technically have any amount of air, so we can TEST a Value. Instead of randomly choosing a number, you should take a quick look at the answer choices. Notice how the common-denominator is 16? That number will likely be the best choice for your starting value.

Now, all you have to do is the basic "math", removing half after each stroke (with 4 strokes total):

Start = 16
remove half = 16 - 8 = 8
remove half = 8 - 4 = 4
remove half = 4 - 2 = 2
remove half = 2 - 1 - 1

So, 1/16 is left and 15/16 is removed.

GMAT assassins aren't born, they're made,
Rich
Contact Rich at [email protected]
Image
Top
Join the discussion
Log in to postLogin with Googleuse password
QUOTE IN REPLY
Post new topic Post Reply
• Page 1 of 1