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The concentration of a certain chemical in a full water tank [#permalink]
16 Nov 2005, 17:58

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Difficulty:

25% (low)

Question Stats:

83% (02:23) correct
16% (02:55) wrong based on 31 sessions

The concentration of a certain chemical in a full water tank depends on the depth of the water. At a depth that is x feet below the top of the tank, the concentration is 3 + \frac{4}{\sqrt{5-x}} parts per million, where 0 < x < 4. To the nearest 0.1 foot, at what depth is the concentration equal to 6 parts per million?

(A) 2.4 ft (B) 2.5 ft (C) 2.8 ft (D) 3.0 ft (E) 3.2 ft

I was going to go with 3.0...but then the question says witin 0.1 feet...and with 3.0..we get within 0.2 feet...so I would have just picked 3.2 at that point....

Re: Problem Solving Proportion [#permalink]
16 Nov 2005, 18:49

joemama142000 wrote:

The concentration of a certain chemical in a full water tank depends on the depth of the water. At a depth that is x feet below the top of the tank, the concentration is 3 + 4/sqrt(5-x) parts per million, where 0< x < 4. To the nearest 0.1 foot, at what depth is the concentration equal to 6 parts per million?

I was going to go with 3.0...but then the question says witin 0.1 feet...and with 3.0..we get within 0.2 feet...so I would have just picked 3.2 at that point.... anyway 4/sqrt(5-x)=3 16/(5-x)=9 16=45-9x solve for X...

not yet...its raining here...and I want to go to the gym

to go or not to go to gym is the question...what would GSR do?hmm

gsr wrote:

fresinha12 wrote:

I was going to go with 3.0...but then the question says witin 0.1 feet...and with 3.0..we get within 0.2 feet...so I would have just picked 3.2 at that point.... anyway 4/sqrt(5-x)=3 16/(5-x)=9 16=45-9x solve for X...

Re: The concentration of a certain chemical in a full water tank [#permalink]
01 Mar 2014, 12:11

My brain is cloudy, going to gym to clear it up....but how did you guys know to set the equation equal to 6? Once we get to the equation the math is easy but I did not know where to begin. Can someone explain?
_________________

Re: The concentration of a certain chemical in a full water tank [#permalink]
02 Mar 2014, 03:40

Expert's post

PeterHAllen wrote:

The concentration of a certain chemical in a full water tank depends on the depth of the water. At a depth that is x feet below the top of the tank, the concentration is 3 + \frac{4}{\sqrt{5-x}} parts per million, where 0 < x < 4. To the nearest 0.1 foot, at what depth is the concentration equal to 6 parts per million?

(A) 2.4 ft (B) 2.5 ft (C) 2.8 ft (D) 3.0 ft (E) 3.2 ft

My brain is cloudy, going to gym to clear it up....but how did you guys know to set the equation equal to 6? Once we get to the equation the math is easy but I did not know where to begin. Can someone explain?

Given: at a depth that is x feet below the top of the tank, the concentration is 3 + \frac{4}{\sqrt{5-x}} parts per million.

Question: at what depth, for which x, is the concentration equal to 6 parts per million? So, for which x, is 3 + \frac{4}{\sqrt{5-x}} equal to 6?