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The cost C, in dollars, to remove p percent of a certain pollutant fro
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18 Oct 2015, 12:15
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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.
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The cost C, in dollars, to remove p percent of a certain pollutant fro
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Updated on: 25 Nov 2017, 14:03
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.
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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro
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18 Oct 2015, 12:30
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. Cost to remove 90%  Cost to remove 80% = 100,000*90/(100  90)  100,000*80/(100  80) = 9*100,000  4*100,000 = 5*100,000 =500,000 Ans A



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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro
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18 Oct 2015, 21:19
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. required cost = (100,000 * 90)/(100  90)  (100,000 * 80) /(100  80) = 100,000 * (90/10  80/20) = 100,000 * (9  4) = 100,000 * (5) = 500,000 answer choice A



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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro
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19 Oct 2015, 09:28
Hii,
Instead of putting 80 or 90 as P, will we not put 80% or 90% as P.
Kind Regards, Richa



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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro
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19 Oct 2015, 18:14
It has to be A...
C = (100000*p)/100p Here we can check puuting the values for 90 and 80 i.e.
Let 100000 be x so for 90 its => 90x/10 =>9x 1
for 80 its => 80x/20 =>4x 2
Now , subtracting 2 from 1 we get => 9x  4x = 5x or 5*100000 => 500,000



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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro
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19 Oct 2015, 20:49
To remove 90% of pollutant C= 100,000(90)/(10090) = 900,000
To remove 80% of pollutant C' = 100,000(80)/(10080) = 400,000
Difference = C  C' = 500,000
Answer  A



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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro
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28 Oct 2015, 04:42
Richa07 wrote: Hii,
Instead of putting 80 or 90 as P, will we not put 80% or 90% as P.
Kind Regards, Richa Would this approach be wrong? I know it would make our calculations whole a lot more difficult, but one could put in as P 0.9 and 0.8 at the beginning and after throwing away 30 seconds only realise the flaw in the approach. But would this also be wrong mathematically? Thanks, Jay



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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro
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02 May 2016, 14:35
Trick here is to not think too hard about it. p doesn't need to be expressed as a fraction or a decimal
just plug and play. 90%80% difference (first do 90, then do 80, and subtract)
90% : 100,000(90)/(10) = 900,000
80% : 100,000(80)/(20) = 400,000
94 = 5*100,000



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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro
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03 May 2016, 04:38
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. 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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The cost C, in dollars, to remove p percent of a certain pollutant fro
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07 Dec 2016, 19:15
Attached is a visual that should help. In order to solve this question correctly, you must realize that p is expressed as a percent and thus should not be converted to a decimal.
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Screen Shot 20161207 at 7.14.39 PM.png [ 129.25 KiB  Viewed 12799 times ]
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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro
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21 Jan 2017, 08:06
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.
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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro
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05 Feb 2017, 21:07
Richa07 wrote: Hii,
Instead of putting 80 or 90 as P, will we not put 80% or 90% as P.
Kind Regards, Richa Richa07 , do you know why we should approach this exercises as such?
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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro
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06 Feb 2017, 08:43
Cost to remove 90% = 900,000 Cost to remove 80% = 400,000
Excess cost = 900,000400,000 =500,000



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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro
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12 Mar 2017, 07:28
done in a minute!:
(100 000*90)/10  (100 000*80)/20=100 000*(94)=500 000$



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Re: The cost C, in dollars, to remove p percent of a certain pollutant fro
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16 Sep 2018, 04:21
Hi all,
Why is it not correct to take p= 10 as in the difference between 90 and 80 will be 10 percent?
Thanks!
Posted from my mobile device



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The cost C, in dollars, to remove p percent of a certain pollutant fro
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17 Sep 2018, 08:38
Lionila wrote: Hi all,
Why is it not correct to take p= 10 as in the difference between 90 and 80 will be 10 percent?
Thanks!
Posted from my mobile device Because in this case cost is not directly proportional to the %, hence % change will not give you the same change in cost. E.g. You can buy 1 phone for $100 or 2 for $150 per promo  you get 2 times the phones, but pay 1.5 time the price.




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