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

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Difficulty:

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Question Stats:

63% (01:48) correct
37% (00:44) wrong based on 186 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 ?

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$$.

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?

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

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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.

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

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srivats212 wrote:

Could someone please help me out with the below problem:

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

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

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. _________________

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

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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 ?

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