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The cost C

This topic has 6 expert replies and 1 member reply
shahfahad Senior | Next Rank: 100 Posts Default Avatar
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The cost C

Post Thu Nov 26, 2015 1:52 am
The cost C, in dollars, to remove p percent of a certain pollutant from a pond is estimated by using the formula C=100,000p/100-p. According to the estimate, how much more would it cost to remove 90% of the pollutant from the pond than it would cost to remove 80% of the pollutant?

(A) $500,000
(B) $100,000
(C) $50,000
(D) $10,000
(E) $5,000

I solved the question first with 90%-80% = 10% method but it did not work. Then i calculated them separately and subtracted them and got the right answer. Why doesn't the 10% value works as it is the difference between 90 and 80%.

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Post Mon Aug 01, 2016 9:18 am
Hi rqmantovani,

The given equation expects us to plug in a value for P. The variable "P" will have to be a number (between 0 and 100, inclusive) since it's described in the context of "...P percent of a certain pollutant..."

IF... P = 90, then the sentence reads.... "to remove 90 percent of a certain pollutant..."
IF...P = .9, then the sentence reads... "to remove .9 percent of a certain pollutant..."

Given the wording of the rest of the prompt, we're expected to plug in P = 90 (and also P = 80) and complete the given calculations.

GMAT assassins aren't born, they're made,
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Post Mon Aug 01, 2016 3:38 pm
shahfahad wrote:
The cost C, in dollars, to remove p percent of a certain pollutant from a pond is estimated by using the formula C=100,000p/100-p. According to the estimate, how much more would it cost to remove 90% of the pollutant from the pond than it would cost to remove 80% of the pollutant?

(A) $500,000
(B) $100,000
(C) $50,000
(D) $10,000
(E) $5,000
Here is my take:

The cost to remove 90 percent of the pollutant is determined by letting p = 90 in the cost formula:

100,000(90)/(100 - 90) = 9,000,000/10 = 900,000

Similarly, the cost to remove 80 percent of the pollutant is determined by letting p = 80 in the cost formula:

100,000(80)/(100 - 80) = 8,000,000/20 = 400,000

To determine how much more it costs to remove 90 percent of the pollutant than 80 percent of the pollutant, we calculate the difference of the two costs:

900,000 - 400,000 = 500,000

Answer: A

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Post Mon Aug 01, 2016 9:18 am
Hi rqmantovani,

The given equation expects us to plug in a value for P. The variable "P" will have to be a number (between 0 and 100, inclusive) since it's described in the context of "...P percent of a certain pollutant..."

IF... P = 90, then the sentence reads.... "to remove 90 percent of a certain pollutant..."
IF...P = .9, then the sentence reads... "to remove .9 percent of a certain pollutant..."

Given the wording of the rest of the prompt, we're expected to plug in P = 90 (and also P = 80) and complete the given calculations.

GMAT assassins aren't born, they're made,
Rich

_________________
Contact Rich at Rich.C@empowergmat.com

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Post Mon Aug 01, 2016 3:38 pm
shahfahad wrote:
The cost C, in dollars, to remove p percent of a certain pollutant from a pond is estimated by using the formula C=100,000p/100-p. According to the estimate, how much more would it cost to remove 90% of the pollutant from the pond than it would cost to remove 80% of the pollutant?

(A) $500,000
(B) $100,000
(C) $50,000
(D) $10,000
(E) $5,000
Here is my take:

The cost to remove 90 percent of the pollutant is determined by letting p = 90 in the cost formula:

100,000(90)/(100 - 90) = 9,000,000/10 = 900,000

Similarly, the cost to remove 80 percent of the pollutant is determined by letting p = 80 in the cost formula:

100,000(80)/(100 - 80) = 8,000,000/20 = 400,000

To determine how much more it costs to remove 90 percent of the pollutant than 80 percent of the pollutant, we calculate the difference of the two costs:

900,000 - 400,000 = 500,000

Answer: A

_________________
Jeffrey Miller Head of GMAT Instruction

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Post Thu Aug 04, 2016 8:39 pm
rqmantovani wrote:
If p is 90%, why p=90? Shouldn't it be 0.9?
Since the stem gives it to us as "p percent", and we want "90 percent", we have p = 90, not p = .9. (Be careful not to convert to percentages if the word 'percent' is already attached to the variable!)

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rqmantovani Newbie | Next Rank: 10 Posts
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Post Mon Aug 01, 2016 8:19 am
If p is 90%, why p=90? Shouldn't it be 0.9?

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Post Thu Nov 26, 2015 11:54 pm
We've got

100,000(90)/(100 - 90) - 100,000(80)/(100 - 80),

or

100,000 * (90/10 - 80/20)

or

100,000 * (9 - 4),

so it's A.

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