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The cost C, in dollars, to remove p percent of a certain pollutant fro

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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro  [#permalink]

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New post 02 Jul 2020, 08:47
mcelroytutoring wrote:
diegocml wrote:
After checking the solution for this exercise, it looks quite easy. I just don't understand one thing. Why can I just plug the 90 and the 80 for p in the formula and not 90% (90/100) or 80% (80/100)?

i.e.: 100,000(90/100) / 100 - (90/100)

Thanks a lot.


Hi diegocml, "per cent" means "per hundred." So when I say "90 percent," I am actually saying "90/100". Thus, if you plug the number .9 into this formula, which is already formatted for a percent input (in other words, the equation itself has already taken the division by 100 into account), then it will become .9/100 = .009, which is less than one percent!

Lesson learned: if the question or formula already includes the word "percent," then don't divide by 100, because you will be dividing by 100 twice.


Hello, I don't understand why we should not divide per 100. is it not inconsistent with this other official question ?

https://gmatclub.com/forum/last-sunday-a-certain-store-sold-copies-of-newspaper-a-for-1-00-each-101739.html

Thank you for your answer
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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro  [#permalink]

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New post 09 Jul 2020, 15:36
C=100,000P/100-P (c & P are in $ & %)

find C(p=90%)-C(80%)= ?

C(P=90%)= 100,000*90/(100-90) => $ 900,000
C (p=80%)= 100, 000*80/(100-80) =>$ 400,000

C(p=90%)-C(p=80%) = $500,000

Answer (A)

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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro  [#permalink]

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New post 09 Jul 2020, 16:03
Bunuel 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 this estimate, how much more would it cost to remove 90 percent of the pollutant from the pond than it would cost to remove 80 percent of the pollutant?

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

Kudos for a correct solution.

To remove 90 percent of the pollutant, it would cost = 100,000* 90/ 10 = $900,000
For 80 percent, the cost = 100,000* 80/ 20 =400,000
Difference = $500,000
A is the answer.
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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro   [#permalink] 09 Jul 2020, 16:03

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