• Reach higher with Artificial Intelligence. Guaranteed
Now free for 30 days

Available with Beat the GMAT members only code

• Magoosh
Study with Magoosh GMAT prep

Available with Beat the GMAT members only code

• Get 300+ Practice Questions

Available with Beat the GMAT members only code

• 5-Day Free Trial
5-day free, full-access trial TTP Quant

Available with Beat the GMAT members only code

• Free Trial & Practice Exam
BEAT THE GMAT EXCLUSIVE

Available with Beat the GMAT members only code

• Award-winning private GMAT tutoring
Register now and save up to $200 Available with Beat the GMAT members only code • 1 Hour Free BEAT THE GMAT EXCLUSIVE Available with Beat the GMAT members only code • 5 Day FREE Trial Study Smarter, Not Harder Available with Beat the GMAT members only code • Free Veritas GMAT Class Experience Lesson 1 Live Free Available with Beat the GMAT members only code • Free Practice Test & Review How would you score if you took the GMAT Available with Beat the GMAT members only code The cost C tagged by: Brent@GMATPrepNow This topic has 6 expert replies and 1 member reply shahfahad Senior | Next Rank: 100 Posts Joined 30 Oct 2015 Posted: 42 messages The cost C 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%.

GMAT/MBA Expert

Jeff@TargetTestPrep GMAT Instructor
Joined
09 Apr 2015
Posted:
867 messages
Followed by:
12 members
39
Mon Aug 01, 2016 3:38 pm
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 GMAT/MBA Expert Matt@VeritasPrep GMAT Instructor Joined 12 Sep 2012 Posted: 2637 messages Followed by: 113 members Upvotes: 625 Target GMAT Score: V51 GMAT Score: 780 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!) Enroll in a Veritas Prep GMAT class completely for FREE. Wondering if a GMAT course is right for you? Attend the first class session of an actual GMAT course, either in-person or live online, and see for yourself why so many students choose to work with Veritas Prep. Find a class now! GMAT/MBA Expert Rich.C@EMPOWERgmat.com Elite Legendary Member Joined 23 Jun 2013 Posted: 9297 messages Followed by: 477 members Upvotes: 2867 GMAT Score: 800 Thu Nov 26, 2015 11:07 am Hi shahfahad, If the question expected you to just subtract 80% from 90%, then none of that other information would have been provided. This is an example of a 'Symbolism' question - you're given a formula, and told what it means, and then you're expected to perform a calculation or two with it. The reason why you won't get the correct answer by just subtracting the percents is that those two values impact the given equation in different ways (consider how the denominator changes relative to the numerator when you plug in 80% vs. 90%). GMAT assassins aren't born, they're made, Rich _________________ Contact Rich at Rich.C@empowergmat.com GMAT/MBA Expert Brent@GMATPrepNow GMAT Instructor Joined 08 Dec 2008 Posted: 11393 messages Followed by: 1228 members Upvotes: 5254 GMAT Score: 770 Thu Nov 26, 2015 12:08 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

Cost to remove 90%
p = 90
So, cost = 100,000(90)/(100-90)
= 9,000,000/10 = 900,000

Cost to remove 80%
p = 80
So, cost = 100,000(80)/(100-80)
= 8,000,000/20 = 400,000

DIFFERENCE = 900,000 - 400,000 = \$500,000

Cheers,
Brent

_________________
Brent Hanneson â€“ Founder of GMATPrepNow.com
Use our video course along with

Check out the online reviews of our course
Come see all of our free resources

GMAT Prep Now's comprehensive video course can be used in conjunction with Beat The GMATâ€™s FREE 60-Day Study Guide and reach your target score in 2 months!

GMAT/MBA Expert

Matt@VeritasPrep GMAT Instructor
Joined
12 Sep 2012
Posted:
2637 messages
Followed by:
113 members
625
Target GMAT Score:
V51
GMAT Score:
780
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.

Enroll in a Veritas Prep GMAT class completely for FREE. Wondering if a GMAT course is right for you? Attend the first class session of an actual GMAT course, either in-person or live online, and see for yourself why so many students choose to work with Veritas Prep. Find a class now!
rqmantovani Newbie | Next Rank: 10 Posts
Joined
11 Jan 2015
Posted:
1 messages
Mon Aug 01, 2016 8:19 am
If p is 90%, why p=90? Shouldn't it be 0.9?

GMAT/MBA Expert

Rich.C@EMPOWERgmat.com Elite Legendary Member
Joined
23 Jun 2013
Posted:
9297 messages
Followed by:
477 members
2867
GMAT Score:
800
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

Best Conversation Starters

1 lheiannie07 92 topics
2 Roland2rule 61 topics
3 ardz24 60 topics
4 LUANDATO 59 topics
5 M7MBA 50 topics
See More Top Beat The GMAT Members...

Most Active Experts

1 Rich.C@EMPOWERgma...

EMPOWERgmat

138 posts
2 GMATGuruNY

The Princeton Review Teacher

131 posts
3 Brent@GMATPrepNow

GMAT Prep Now Teacher

122 posts
4 Jeff@TargetTestPrep

Target Test Prep

114 posts
5 Scott@TargetTestPrep

Target Test Prep

100 posts
See More Top Beat The GMAT Experts