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# The concentration of a certain chemical in a full water tank

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Manager
Joined: 06 May 2009
Posts: 74

Kudos [?]: 139 [0], given: 3

The concentration of a certain chemical in a full water tank [#permalink]

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23 Jun 2009, 05:01
00:00

Difficulty:

25% (medium)

Question Stats:

79% (01:34) correct 21% (03:03) wrong based on 78 sessions

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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

OPEN DISCUSSION OF THIS QUESTION IS HERE: the-concentration-of-a-certain-chemical-in-a-full-water-tank-23165.html
[Reveal] Spoiler: OA

Kudos [?]: 139 [0], given: 3

Senior Manager
Joined: 16 Jan 2009
Posts: 354

Kudos [?]: 238 [2], given: 16

Concentration: Technology, Marketing
GMAT 1: 700 Q50 V34
GPA: 3
WE: Sales (Telecommunications)
Re: concentration of certain chemical [#permalink]

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23 Jun 2009, 05:06
2
KUDOS
(3 + (4/sq root (5-x)))=6
(4/sq root (5-x))=3
sq root (5-x)=4/3
x=5-(16/9)
x=3.2
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Lahoosaher

Kudos [?]: 238 [2], given: 16

Manager
Joined: 06 May 2009
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Kudos [?]: 139 [0], given: 3

Re: concentration of certain chemical [#permalink]

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23 Jun 2009, 07:18

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Re: concentration of certain chemical [#permalink]

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10 Apr 2014, 21:07
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Math Expert
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Re: The concentration of a certain chemical in a full water tank [#permalink]

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11 Apr 2014, 04:03
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

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?

$$3 + \frac{4}{\sqrt{5-x}}=6$$ --> $$x\approx{3.2}$$.

OPEN DISCUSSION OF THIS QUESTION IS HERE: the-concentration-of-a-certain-chemical-in-a-full-water-tank-23165.html
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Kudos [?]: 132588 [0], given: 12326

Re: The concentration of a certain chemical in a full water tank   [#permalink] 11 Apr 2014, 04:03
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