A portion of the 85% solution of chemicals was replaced with : GMAT Problem Solving (PS)
Check GMAT Club Decision Tracker for the Latest School Decision Releases https://gmatclub.com/AppTrack

 It is currently 22 Feb 2017, 05:15

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# A portion of the 85% solution of chemicals was replaced with

Author Message
TAGS:

### Hide Tags

CEO
Joined: 21 Jan 2007
Posts: 2756
Location: New York City
Followers: 11

Kudos [?]: 882 [1] , given: 4

A portion of the 85% solution of chemicals was replaced with [#permalink]

### Show Tags

04 Nov 2007, 18:56
1
KUDOS
20
This post was
BOOKMARKED
00:00

Difficulty:

25% (medium)

Question Stats:

79% (02:32) correct 21% (02:03) wrong based on 558 sessions

### HideShow timer Statistics

A portion of the 85% solution of chemicals was replaced with an equal amount of 20% solution of chemicals. As a result, 40% solution of chemicals resulted. What part of the original solution was replaced?

A. 5/13
B. 6/13
C. 9/13
D. 13/9
C. 13/6
[Reveal] Spoiler: OA

Last edited by Bunuel on 24 Mar 2012, 01:52, edited 1 time in total.
Manager
Joined: 26 Sep 2007
Posts: 65
Followers: 1

Kudos [?]: 21 [0], given: 5

### Show Tags

04 Nov 2007, 19:14
Let the original amount of 85 percent solution = x and amount replaced be y
0.85(x - y)+ 0.2y = 0.4 x
0.85x -0.85y+0.2y = 0.4x
0.45x = 0.65y
9x = 13y
y = 9x/13
So, amount replaced = 9/13 of original amount
VP
Joined: 08 Jun 2005
Posts: 1145
Followers: 7

Kudos [?]: 193 [5] , given: 0

### Show Tags

04 Nov 2007, 19:20
5
KUDOS
6
This post was
BOOKMARKED
See attachment

the new ratio is 20:45 = 4:9 ---> meaning that if we had 13ml of 85% solution we now have only 4ml so the part that was replaced is 9/13.

Attachments

Drawing Number 1.GIF [ 2.76 KiB | Viewed 10135 times ]

Retired Moderator
Joined: 18 Jul 2008
Posts: 994
Followers: 10

Kudos [?]: 199 [0], given: 5

### Show Tags

24 Mar 2009, 18:47
Can someone explain to me killer squirrels method? my head is spinning.

Specifically, this part:

meaning that if we had 13ml of 85% solution we now have only 4ml so the part that was replaced is 9/13.

KillerSquirrel wrote:
See attachment

the new ratio is 20:45 = 4:9 ---> meaning that if we had 13ml of 85% solution we now have only 4ml so the part that was replaced is 9/13.

Director
Joined: 01 Apr 2008
Posts: 897
Name: Ronak Amin
Schools: IIM Lucknow (IPMX) - Class of 2014
Followers: 28

Kudos [?]: 657 [0], given: 18

### Show Tags

24 Mar 2009, 21:41
pls visit my post in t55740-ps-intensity-red-paint

hope it helps you to do it in a much easier way

Can someone explain to me killer squirrels method? my head is spinning.

Specifically, this part:

meaning that if we had 13ml of 85% solution we now have only 4ml so the part that was replaced is 9/13.

KillerSquirrel wrote:
See attachment

the new ratio is 20:45 = 4:9 ---> meaning that if we had 13ml of 85% solution we now have only 4ml so the part that was replaced is 9/13.

Manager
Joined: 10 Sep 2009
Posts: 119
Followers: 3

Kudos [?]: 68 [0], given: 10

### Show Tags

12 Nov 2009, 13:05

I haven't seen this kind of picture during my learnings, but it seems to be quite powerful ...
I would appreciate having a better view of your method
Manager
Joined: 17 Aug 2009
Posts: 235
Followers: 5

Kudos [?]: 241 [2] , given: 25

### Show Tags

17 Nov 2009, 21:31
2
KUDOS
2
This post was
BOOKMARKED
A portion of the 85% solution of chemicals was replaced with an equal amount of 20% solution of chemicals. As a result, 40% solution of chemicals resulted. What part of the original solution was replaced?

(1-x)0.85 + .20x = .40
.85 -.85x + .20x = .40
.45=.65x
x=9/13

Alternate way

Let there be x litres of 85% solution initially
Suppose y litres of 85% solution is removed

Then the remaining solution is (x-y).85
Now, equal amount of solution that is replaced(y) is added, therefore => .20y

(x-y).85 + .20y = .40x
.45x = .65y
y=9/13

Hope this helps

Consider kudos for the post
Manager
Joined: 19 Dec 2010
Posts: 145
Followers: 2

Kudos [?]: 30 [3] , given: 12

### Show Tags

12 Mar 2011, 22:31
3
KUDOS
3
This post was
BOOKMARKED
9/13.
The formula for these problems is simple.
Whole - part removed + part added = Total
85% (100) - 85% (X) + 20% (X) = 40% (100)

solve
Director
Status: No dream is too large, no dreamer is too small
Joined: 14 Jul 2010
Posts: 651
Followers: 42

Kudos [?]: 892 [0], given: 39

Re: A portion of the 85% solution of chemicals was replaced with [#permalink]

### Show Tags

14 Dec 2011, 09:37
x part is replaced so 1-x is not replaced
(1-x)0.85+0.20x = 0.40
0.85 - 0.85x + 0.20x = 0.40
0.65x = 0.45
x = 9/13
_________________

Collections:-
PSof OG solved by GC members: http://gmatclub.com/forum/collection-ps-with-solution-from-gmatclub-110005.html
DS of OG solved by GC members: http://gmatclub.com/forum/collection-ds-with-solution-from-gmatclub-110004.html
100 GMAT PREP Quantitative collection http://gmatclub.com/forum/gmat-prep-problem-collections-114358.html
Collections of work/rate problems with solutions http://gmatclub.com/forum/collections-of-work-rate-problem-with-solutions-118919.html
Mixture problems in a file with best solutions: http://gmatclub.com/forum/mixture-problems-with-best-and-easy-solutions-all-together-124644.html

Intern
Joined: 27 Feb 2012
Posts: 37
Followers: 1

Kudos [?]: 21 [0], given: 5

### Show Tags

23 Mar 2012, 11:38
KillerSquirrel wrote:
See attachment

the new ratio is 20:45 = 4:9 ---> meaning that if we had 13ml of 85% solution we now have only 4ml so the part that was replaced is 9/13.

KillerSquirrel,

i follow the Ratio how you calculated and got o 4/9,
and 9+4 = 13 Ml and 85% wold be 4.

but how did you determine that 9 the denominator of 4/9 should go over 13?

I'm very new to these types of math problems
Math Expert
Joined: 02 Sep 2009
Posts: 37076
Followers: 7241

Kudos [?]: 96294 [0], given: 10730

Re: A portion of the 85% solution of chemicals was replaced with [#permalink]

### Show Tags

24 Mar 2012, 02:01
Expert's post
2
This post was
BOOKMARKED
bmwhype2 wrote:
A portion of the 85% solution of chemicals was replaced with an equal amount of 20% solution of chemicals. As a result, 40% solution of chemicals resulted. What part of the original solution was replaced?

A. 5/13
B. 6/13
C. 9/13
D. 13/9
C. 13/6

This is a weighted average question. Say x% of the solution was replaced --> equate the amount of chemicals: 0.85(1-x)+0.2*x=0.4 --> x=9/13.

_________________
Manager
Joined: 28 Jul 2011
Posts: 240
Followers: 4

Kudos [?]: 124 [0], given: 16

Re: A portion of the 85% solution of chemicals was replaced with [#permalink]

### Show Tags

25 Mar 2012, 11:04
Ans C

Solution Replaced = x

85/100(1-x) + 20x/100 = 40/100

85/100 - 85x/100 + 20x/100 = 40/100

85/100 - 65x/100 = 40/100

85/100 - 40/100 = 65x/100

45/100 = 65x/100

45/65 = x
9/13 = x
GMAT Club Legend
Joined: 09 Sep 2013
Posts: 13911
Followers: 589

Kudos [?]: 167 [0], given: 0

Re: A portion of the 85% solution of chemicals was replaced with [#permalink]

### Show Tags

09 Oct 2013, 17:42
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
Manager
Joined: 23 May 2013
Posts: 127
Followers: 1

Kudos [?]: 55 [0], given: 110

Re: A portion of the 85% solution of chemicals was replaced with [#permalink]

### Show Tags

18 Oct 2013, 20:35
i like the allegation way of resolving problems

We all will get to the point - that to achieve 40% of solution, we need to have 4 parts of 85% sol and 9 part of 20% solution. Question asks how many part of 85% was removed? We had to remove 9/13 parts of 85% solution.

If its difficult to understand, imagine a container full of 85% solution or we have 13 parts of it. Now we keep replacing 85% with 20% solution till the time it reaches 40%. We know that in final solution both will be in ratio of 4:9. How much did we remove? We need to remove 9 parts of 85% solution.
_________________

“Confidence comes not from always being right but from not fearing to be wrong.”

Senior Manager
Joined: 20 Dec 2013
Posts: 273
Location: India
Followers: 0

Kudos [?]: 85 [0], given: 29

Re: A portion of the 85% solution of chemicals was replaced with [#permalink]

### Show Tags

05 Oct 2014, 06:43
I reached the solution this way:
Let there be 2 solutions: S1-100 units containing 85 u chemical
S2-100 units containing 20 units of chemical
We're given:85-0.85x+0.20x=40u
Solving the equation we get 9/13%.
(Note:-Whatever quantity of S1 or S2 we take out, say x in this case, will contain 85% and 20% of chemicals only)
Current Student
Joined: 26 Aug 2014
Posts: 827
Concentration: Marketing
GMAT 1: 680 Q V
GPA: 3.4
Followers: 7

Kudos [?]: 159 [0], given: 98

Re: A portion of the 85% solution of chemicals was replaced with [#permalink]

### Show Tags

06 Oct 2014, 09:25
I kind of got confused with 85% solution....85% of what? Is the question saying that 85% of the solution is made up of chemicals?? it was hard for me to visualize what the question was actually asking
SVP
Status: The Best Or Nothing
Joined: 27 Dec 2012
Posts: 1858
Location: India
Concentration: General Management, Technology
WE: Information Technology (Computer Software)
Followers: 49

Kudos [?]: 1985 [0], given: 193

A portion of the 85% solution of chemicals was replaced with [#permalink]

### Show Tags

07 Oct 2014, 23:58
angelfire213 wrote:
I kind of got confused with 85% solution....85% of what? Is the question saying that 85% of the solution is made up of chemicals?? it was hard for me to visualize what the question was actually asking

Take it in this way.....

Solution I >> 85% solution of chemicals

Solution II >> 20% solution of chemicals

Resultant Mixture >> 40% solution of chemicals

"Replacement" of Solution I means "Addition" of Solution II. They are asking how much Solution II is added?

I used method of allegation for this as shown in above posts; works perfect
_________________

Kindly press "+1 Kudos" to appreciate

Director
Joined: 23 Jan 2013
Posts: 582
Schools: Cambridge'16
Followers: 1

Kudos [?]: 21 [1] , given: 40

Re: A portion of the 85% solution of chemicals was replaced with [#permalink]

### Show Tags

22 Oct 2014, 02:17
1
KUDOS
Differential approach is:

85-------40-----20

45x=20y
x/y=20/45=4/9 meaning that final solution (40%) have 4 part of 85% (original) and 9 part of 20%.
So, 9/13 was replaced

Weigthed mean:

85x+20y/x+y=40
85x+20y=40x+40y
45x=20y
x/y=4/9, so the same as above

C
GMAT Club Legend
Joined: 09 Sep 2013
Posts: 13911
Followers: 589

Kudos [?]: 167 [0], given: 0

Re: A portion of the 85% solution of chemicals was replaced with [#permalink]

### Show Tags

23 Nov 2015, 23:41
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
Director
Joined: 07 Dec 2014
Posts: 549
Followers: 3

Kudos [?]: 97 [0], given: 3

Re: A portion of the 85% solution of chemicals was replaced with [#permalink]

### Show Tags

04 Apr 2016, 15:21
let x=part of original solution replaced
.85-.85x+.2x=.4
x=45/65=9/13
Re: A portion of the 85% solution of chemicals was replaced with   [#permalink] 04 Apr 2016, 15:21

Go to page    1   2    Next  [ 28 posts ]

Similar topics Replies Last post
Similar
Topics:
8 A certain quantity of 40% concentration solution is replaced 7 21 Jan 2015, 08:11
20 10% of a 50% alcohol solution is replaced with water 11 25 Oct 2014, 21:53
64 One-fourth of a solution that was 10% by weight was replaced 22 13 Mar 2013, 12:52
74 If a portion of a half water/half alcohol mix is replaced 41 02 Sep 2010, 07:24
18 Some part of a 50% solution of acid was replaced with an 16 12 Aug 2008, 13:27
Display posts from previous: Sort by