Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 18 Sep 2014, 14:06

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# If 1/2 of the air in a tank is removed with each stroke of a

Author Message
TAGS:
Manager
Joined: 23 Mar 2008
Posts: 226
Followers: 1

Kudos [?]: 13 [0], given: 0

If 1/2 of the air in a tank is removed with each stroke of a [#permalink]  24 Jun 2008, 12:16
1
This post was
BOOKMARKED
00:00

Difficulty:

35% (medium)

Question Stats:

62% (01:52) correct 38% (00:45) wrong based on 130 sessions
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
[Reveal] Spoiler: OA

Last edited by Bunuel on 13 May 2014, 05:32, edited 1 time in total.
Renamed the topic, edited the question, added the OA and moved to PS forum.
SVP
Joined: 30 Apr 2008
Posts: 1893
Location: Oklahoma City
Schools: Hard Knocks
Followers: 29

Kudos [?]: 433 [0], given: 32

Re: tank [#permalink]  24 Jun 2008, 12:18
A

First you have 1

so
first stroke = 1/2
second stroke = 1/4
third stroke = 1/8
fourth stroke = 1/16

8/16 + 4/16 + 2/16 + 1/16 = 15/16

puma 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 the air has been removed after 4 strokes?

A) 15/16
B) 7/8
C) 1/4
D) 1/8
E) 1/16

_________________

------------------------------------
J Allen Morris
**I'm pretty sure I'm right, but then again, I'm just a guy with his head up his a.

Intern
Joined: 30 Jul 2007
Posts: 35
Followers: 0

Kudos [?]: 1 [1] , given: 0

Re: tank [#permalink]  24 Jun 2008, 12:58
1
KUDOS
puma 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 the air has been removed after 4 strokes?

A) 15/16
B) 7/8
C) 1/4
D) 1/8
E) 1/16

I get A, too.

Let X = air in the tank.

Plug in 240 = X.

First stroke = 1/2 * 240 = 120
Second stroke = 1/2 * 120 = 60
Third stroke = 1/2 * 60 = 30
Fourth stroke = 1/2 * 30 = 15

So 15 remains, which is the amount of air left.

240 - 15 = 225 (amount of air removed). 225/240 = 15/16
Intern
Joined: 04 May 2011
Posts: 12
Followers: 0

Kudos [?]: 1 [1] , given: 11

If 1/2 of the air in a tank is removed with each stroke of a [#permalink]  09 Jun 2011, 10:26
1
KUDOS
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

This question is actually from the OG 12th edition. Am not able to understand the explanation given in OG for this problem. Could someone please explain in detail as to how to solve this

Last edited by Bunuel on 24 Sep 2013, 01:43, edited 1 time in total.
Renamed the topic and edited the question.
Current Student
Joined: 26 May 2005
Posts: 571
Followers: 18

Kudos [?]: 110 [1] , given: 13

Re: Need Help - Fractions [#permalink]  09 Jun 2011, 10:49
1
KUDOS
srivats212 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

This question is actually from the OG 12th edition. Am not able to understand the explanation given in OG for this problem. Could someone please explain in detail as to how to solve this

The best thing to do here is plug in
Assume that there is 16 units of air in the tank
first stroke = 1/2*16 = 8 ( we are left ith 8 now)
second stroke = 1/2*8 = 4( left ith 4 units now)
third stoke = 1/2*4 = 2( left with 2 units)
4th stroke = 1/2* 2 = 1 (left with 1 unit)

total units removed = 8+4+2+1 = 15
total unis in the tank at the begining = 16
thus its A . 15/16

Hope this helps
Manager
Joined: 27 Apr 2008
Posts: 191
Followers: 1

Kudos [?]: 29 [1] , given: 1

Re: Need Help - Fractions [#permalink]  09 Jun 2011, 10:52
1
KUDOS
This is a decay-type problem...the tank is halved after each stroke. Therefore:

(0.5)^4 = 1/16 --> 0.5 for halving, 4 for strokes

so 1/16 of air is left in the tank => 15/16 of the air was removed
Intern
Joined: 04 May 2011
Posts: 12
Followers: 0

Kudos [?]: 1 [0], given: 11

Re: Need Help - Fractions [#permalink]  09 Jun 2011, 11:10
Oh, I get it..! Thanks..!!!
I think the catch over here is.."the tank is halved after each stroke"....failed to understand the question properly.
Thought that a single stoke halves the air in it...so after 2 strokes guessed there wont be any air in it
Manager
Joined: 08 Sep 2010
Posts: 171
Followers: 0

Kudos [?]: 15 [0], given: 18

Re: Need Help - Fractions [#permalink]  09 Jun 2011, 20:30
A - 15/16..

Left After 1st stroke = 1/2
Left After 2nd stroke = 1/2 * 1/2 = 1/4
Left After 3rd stroke = 1/2 * 1/4 = 1/8
Left After 4th stroke = 1/2 * 1/8 = 1/16

So removed = 1- 1/16 = 15/16
_________________

My will shall shape the future. Whether I fail or succeed shall be no man's doing but my own.

If you like my explanations award kudos.

Manager
Joined: 27 Apr 2008
Posts: 191
Followers: 1

Kudos [?]: 29 [0], given: 1

Re: Need Help - Fractions [#permalink]  10 Jun 2011, 08:40
As they say, the devil is in the details!
Senior Manager
Joined: 12 Oct 2009
Posts: 272
Followers: 2

Kudos [?]: 33 [0], given: 4

Re: Need Help - Fractions [#permalink]  10 Jun 2011, 10:42
By the 4th stroke the the air remaining is 1/16 , so what has been removed is 15/16
Manager
Joined: 05 Oct 2011
Posts: 169
GMAT 1: 720 Q V
Followers: 7

Kudos [?]: 34 [0], given: 60

Re: tank [#permalink]  02 Nov 2011, 09:44
1st stroke 1/2
2nd stroke 1/4
3rd stroke 1/8
4th stroke 1/16
total: (8+4+2+1)/16=15/16
Manager
Joined: 05 Oct 2011
Posts: 169
GMAT 1: 720 Q V
Followers: 7

Kudos [?]: 34 [0], given: 60

Re: Need Help - Fractions [#permalink]  02 Nov 2011, 09:46
1st stroke 1/2
2nd stroke 1/4
3rd stroke 1/8
4th stroke 1/16
total: (8+4+2+1)/16=15/16
Verbal Forum Moderator
Joined: 22 Mar 2013
Posts: 915
Location: India
GPA: 3.51
WE: Information Technology (Computer Software)
Followers: 31

Kudos [?]: 326 [0], given: 194

Re: Need Help - Fractions [#permalink]  24 Sep 2013, 01:31
Better use compound interest formula.

Remaing amount = P ( 1 - R/100)^n

Let P is 100 ( 1 - 50/100)^4
Remaining amount = 100(1/16)

if 1/16 of 100 is remaining means 1-1/16 = 15/16 is lost.
_________________

Piyush K
-----------------------
Our greatest weakness lies in giving up. The most certain way to succeed is to try just one more time. ― Thomas A. Edison
Don't forget to press--> Kudos
My Articles: 1. WOULD: when to use? | 2. All GMATPrep RCs (New)
Tip: Before exam a week earlier don't forget to exhaust all gmatprep problems specially for "sentence correction".

SVP
Joined: 09 Sep 2013
Posts: 2420
Followers: 196

Kudos [?]: 38 [0], given: 0

Re: if 1/2 of the air in a tank is removed with each stroke of a [#permalink]  13 May 2014, 04:31
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
Math Expert
Joined: 02 Sep 2009
Posts: 29680
Followers: 3497

Kudos [?]: 26371 [0], given: 2710

Re: If 1/2 of the air in a tank is removed with each stroke of a [#permalink]  13 May 2014, 05:32
Expert's post
puma 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

Similar questions to practice:
if-2-3-of-the-air-in-a-tank-is-removed-with-each-stroke-of-a-128432.html
if-3-4-of-the-mineral-deposits-in-a-reservoir-of-water-are-97300.html
on-january-1-2076-lake-loser-contains-x-liters-of-water-b-82667.html

Hope it helps.
_________________
Director
Status: The Best Or Nothing
Joined: 27 Dec 2012
Posts: 925
Location: India
Concentration: General Management, Technology
WE: Information Technology (Computer Software)
Followers: 6

Kudos [?]: 237 [0], given: 167

Re: If 1/2 of the air in a tank is removed with each stroke of a [#permalink]  31 Jul 2014, 23:57
Let say total air = 1

Total air removed

= \frac{1}{2} + \frac{1}{2^2} + \frac{1}{2^3} + \frac{1}{2^4}

= \frac{15}{16}

_________________

Kindly press "+1 Kudos" to appreciate

Re: If 1/2 of the air in a tank is removed with each stroke of a   [#permalink] 31 Jul 2014, 23:57
Similar topics Replies Last post
Similar
Topics:
6 While they remove carbon dioxide from the air 5 17 Jul 2012, 18:29
8 If 2/3 of the air in a tank is removed with each stroke of a 5 01 Mar 2012, 15:58
If 1/2 of the air in a tank is removed with each stroke of a 0 24 Sep 2013, 01:44
If of the air in a tank is removed with each stroke of a 4 07 Aug 2007, 21:46
If 1/2 of the air in a tank is removed with each stroke of a 4 16 Jan 2005, 11:26
Display posts from previous: Sort by