If 1/2 of the air in a tank is removed with each stroke of a : GMAT Problem Solving (PS)
Check GMAT Club Decision Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 23 Jan 2017, 14:33

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:

Hide Tags

Manager
Joined: 23 Mar 2008
Posts: 219
Followers: 3

Kudos [?]: 143 [1] , given: 0

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

Show Tags

24 Jun 2008, 12:16
1
KUDOS
5
This post was
BOOKMARKED
00:00

Difficulty:

35% (medium)

Question Stats:

60% (01:52) correct 40% (00:47) wrong based on 410 sessions

HideShow timer Statistics

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: 1887
Location: Oklahoma City
Schools: Hard Knocks
Followers: 40

Kudos [?]: 571 [0], given: 32

Show Tags

24 Jun 2008, 12:18
1
This post was
BOOKMARKED
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.

GMAT Club Premium Membership - big benefits and savings

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

Kudos [?]: 2 [1] , given: 0

Show Tags

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: 11
Followers: 0

Kudos [?]: 3 [1] , given: 11

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

Show Tags

09 Jun 2011, 10:26
1
KUDOS
1
This post was
BOOKMARKED
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: 565
Followers: 18

Kudos [?]: 204 [3] , given: 13

Re: Need Help - Fractions [#permalink]

Show Tags

09 Jun 2011, 10:49
3
KUDOS
1
This post was
BOOKMARKED
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: 190
Followers: 1

Kudos [?]: 77 [1] , given: 1

Re: Need Help - Fractions [#permalink]

Show Tags

09 Jun 2011, 10:52
1
KUDOS
1
This post was
BOOKMARKED
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: 11
Followers: 0

Kudos [?]: 3 [0], given: 11

Re: Need Help - Fractions [#permalink]

Show Tags

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: 166
Followers: 0

Kudos [?]: 23 [0], given: 18

Re: Need Help - Fractions [#permalink]

Show Tags

09 Jun 2011, 20:30
1
This post was
BOOKMARKED
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: 190
Followers: 1

Kudos [?]: 77 [0], given: 1

Re: Need Help - Fractions [#permalink]

Show Tags

10 Jun 2011, 08:40
As they say, the devil is in the details!
Senior Manager
Joined: 12 Oct 2009
Posts: 268
Followers: 4

Kudos [?]: 155 [0], given: 4

Re: Need Help - Fractions [#permalink]

Show Tags

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: 171
Followers: 9

Kudos [?]: 51 [0], given: 62

Show Tags

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: 171
Followers: 9

Kudos [?]: 51 [0], given: 62

Re: Need Help - Fractions [#permalink]

Show Tags

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
Current Student
Status: Everyone is a leader. Just stop listening to others.
Joined: 22 Mar 2013
Posts: 992
Location: India
GPA: 3.51
WE: Information Technology (Computer Software)
Followers: 164

Kudos [?]: 1470 [0], given: 227

Re: Need Help - Fractions [#permalink]

Show Tags

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".

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 13522
Followers: 577

Kudos [?]: 163 [0], given: 0

Re: if 1/2 of the air in a tank is removed with each stroke of a [#permalink]

Show Tags

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: 36618
Followers: 7100

Kudos [?]: 93565 [1] , given: 10578

Re: If 1/2 of the air in a tank is removed with each stroke of a [#permalink]

Show Tags

13 May 2014, 05:32
1
KUDOS
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.
_________________
SVP
Status: The Best Or Nothing
Joined: 27 Dec 2012
Posts: 1858
Location: India
Concentration: General Management, Technology
WE: Information Technology (Computer Software)
Followers: 47

Kudos [?]: 1937 [0], given: 193

Re: If 1/2 of the air in a tank is removed with each stroke of a [#permalink]

Show Tags

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

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 13522
Followers: 577

Kudos [?]: 163 [0], given: 0

Re: If 1/2 of the air in a tank is removed with each stroke of a [#permalink]

Show Tags

26 Oct 2015, 09:19
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.
_________________
Re: If 1/2 of the air in a tank is removed with each stroke of a   [#permalink] 26 Oct 2015, 09:19
Similar topics Replies Last post
Similar
Topics:
10 A group of 3 small pumps and 1 large pump is filling a tank. Each of t 3 01 Nov 2014, 09:39
12 If 2/3 of the air in a tank is removed with each stroke of a 6 01 Mar 2012, 15:58
2 When 200 gallons of oil were removed from a tank 5 25 Mar 2009, 22:05
A bag contains 12 red marbles. If someone were to remove 2 11 07 Aug 2011, 09:56
If of the air in a tank is removed with each stroke of a 4 07 Aug 2007, 21:46
Display posts from previous: Sort by