|
Author |
Message |
|
TAGS:
|
|
|
Intern
Joined: 28 May 2010
Posts: 43
Followers: 0
Kudos [?]:
2
[1] , given: 15
|
The total cost of producing item X is equal to the sum of [#permalink]
 18 Jul 2010, 20:54
1
This post received
KUDOS
Question Stats:
60% (02:02) correct
39% (01:31) wrong based on 2 sessions
The total cost of producing item X is equal to the sum of item X's fixed cost and variable cost. If the variable cost of producing X decreased by 5% in January, by what percent did the total cost of producing item X change in January? (1) The fixed cost of producing item X increased by 13% in January. (2) Before the changes in January, the fixed cost of producing item X was 5 times the variable cost of producing item X. ----------- My question is, why isn't the answer B? The prompt didn't say fixed cost MUST change...
|
|
|
|
|
|
|
GMAT Club team member
Joined: 02 Sep 2009
Posts: 11516
Followers: 1791
Kudos [?]:
9536
[5] , given: 826
|
Re: very hard - MGMAT [#permalink]
18 Jul 2010, 21:44
5
This post received
KUDOS
knabi wrote: The total cost of producing item X is equal to the sum of item X's fixed cost and variable cost. If the variable cost of producing X decreased by 5% in January, by what percent did the total cost of producing item X change in January?
(1) The fixed cost of producing item X increased by 13% in January.
(2) Before the changes in January, the fixed cost of producing item X was 5 times the variable cost of producing item X.
-----------
My question is, why isn't the answer B? The prompt didn't say fixed cost MUST change... (2) is not sufficient as we don't know what happened with fixed cost in January. Didi it increase? Decrease? Remained the same? As we have no information about it we can not assume anything. So it's clear C. Below is calculations for C: Let the total cost in January be C_2 and the total cost before be C_1. Given: C_2=F_2+V_2 and C_1=F_1+V_1, also V_2=0.95V_1. Question: \frac{C_2}{C_1}=\frac{F_2+V_2}{F_1+V_1}=\frac{F_2+0.95V_1}{F_1+V_1}=?(1) The fixed cost of producing item X increased by 13% in January --> F_2=1.13F_1 --> \frac{1.13F_1+0.95V_1}{F_1+V_1}=?. Not sufficient to get the exact fraction. (2) Before the changes in January, the fixed cost of producing item X was 5 times the variable cost of producing item X --> F_1=5V_1 --> \frac{F_2+0.95V_1}{5V_1+V_1}=?. Not sufficient. (1)+(2) F_2=1.13F_1 and F_1=5V_1 --> F_2=1.13F_1=5.65V_1 --> from (2) \frac{F_2+0.95V_1}{F_1+V_1}=? --> substituting F_2 and F_1--> \frac{5.65V_1+0.95V_1}{5V_1+V_1}=\frac{6.6}{6}=1.1 --> in January total cost increased by 10%. Sufficient. (Actually no calculations are needed: stem and statement provide us with such relationships of 4 unknowns that 3 of them can be written with help of the 4th one and when we put them in fraction, which we want to calculate, then this last unknown is reduced, leaving us with numerical value). Answer: C. Hope it's clear.
_________________
PLEASE READ AND FOLLOW: 11 Rules for Posting!!!
RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory
COLLECTION OF QUESTIONS:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. NEW!!!
DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS ; 9 Devil's Dozen!!!; 10 Number Properties set. NEW!!!
What are GMAT Club Tests?
25 extra-hard Quant Tests
Find out what's new at GMAT Club - latest features and updates
|
|
|
|
|
|
Intern
Joined: 28 May 2010
Posts: 43
Followers: 0
Kudos [?]:
2
[0], given: 15
|
Re: very hard - MGMAT [#permalink]
18 Jul 2010, 21:57
great explanation! thanks - kudos.
|
|
|
|
|
|
Intern
Joined: 25 Sep 2010
Posts: 25
Followers: 0
Kudos [?]:
0
[0], given: 7
|
DS question : need help [#permalink]
28 Oct 2010, 14:43
The total cost of producing item X is equal to the sum of item X's fixed cost and variable cost. If the variable cost of producing X decreased by 5% in January, by what percent did the total cost of producing item X change in January?
(1) The fixed cost of producing item X increased by 13% in January.
(2) Before the changes in January, the fixed cost of producing item X was 5 times the variable cost of producing item X.
|
|
|
|
|
|
VP
Status: There is always something new !!
Affiliations: PMI,QAI Global,eXampleCG
Joined: 08 May 2009
Posts: 1400
Followers: 8
Kudos [?]:
84
[0], given: 10
|
Re: very hard - MGMAT [#permalink]
05 May 2011, 22:24
a c1= f+v c2 = kf + 0.95v k = 1.13. no relative information between f and v. Not sufficient. b f=5v c1= 6v. not sufficient. a+b gives c1 = 6v and c2 = 1.13 * 5v + 0.95 v thus C
_________________
Visit -- http://www.sustainable-sphere.com/
Promote Green Business,Sustainable Living and Green Earth !!
|
|
|
|
|
|
Intern
Status: ThinkTank
Joined: 07 Mar 2009
Posts: 29
Followers: 0
Kudos [?]:
5
[0], given: 3
|
Re: very hard - MGMAT [#permalink]
06 May 2011, 09:17
To get the percentage change, we need two of the three in the same units: original, change or new. Both statements give us original and new in terms of y so it is sufficient. But 2) alone gives only original in terms of y and 1) gives new fixed cost but the total new is in different units. Combining both in same unit gives us percentage change.
_________________
http://www.hannibalprep.com
|
|
|
|
|
|
Director
Joined: 03 Feb 2011
Posts: 944
Followers: 9
Kudos [?]:
137
[1] , given: 121
|
Re: very hard - MGMAT [#permalink]
06 May 2011, 21:52
1
This post received
KUDOS
Karishma Pls can you verify this solution. I think this is a weighted average problem.  Combining 1) + 2) 13% increase in the fixed cost and 5% is decrease in variable cost. We know that the weights w1 : w2 are 5 : 1 i.e. Fixed cost : Variable cost = 5 : 1 Hence the %age in the total cost = (13 * w1 - 5 * w2) / (w1 + w2) %change in total cost = (13 * 5 - 5 * 1) / (5 + 1) = 60/ 6 = 10% increase knabi wrote: The total cost of producing item X is equal to the sum of item X's fixed cost and variable cost. If the variable cost of producing X decreased by 5% in January, by what percent did the total cost of producing item X change in January?
(1) The fixed cost of producing item X increased by 13% in January.
(2) Before the changes in January, the fixed cost of producing item X was 5 times the variable cost of producing item X.
Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
Both statements TOGETHER are sufficient, but NEITHER one ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.
-----------
My question is, why isn't the answer B? The prompt didn't say fixed cost MUST change...
|
|
|
|
|
|
SVP
Joined: 16 Nov 2010
Posts: 1721
Location: United States (IN)
Concentration: Strategy, Technology
Followers: 26
Kudos [?]:
227
[0], given: 34
|
Re: very hard - MGMAT [#permalink]
07 May 2011, 05:48
(1) X1 = 1.13F + 0.95V Not sufficient (2) F = 5V => X = 6V X1 = F1 + V1 but we don't know by how much F and V have changed (1) + (2) gives X1 = 1.13F + 0.95V = 1.13 * 5V + 0.95V So (X1-X)/X can be found Answer - C
_________________
Formula of Life -> Achievement/Potential = k * Happiness (where k is a constant)
Find out what's new at GMAT Club - latest features and updates
|
|
|
|
|
|
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 3105
Location: Pune, India
Followers: 567
Kudos [?]:
1995
[1] , given: 92
|
Re: very hard - MGMAT [#permalink]
07 May 2011, 11:13
1
This post received
KUDOS
gmat1220 wrote: Karishma Pls can you verify this solution. I think this is a weighted average problem. Combining 1) + 2) 13% increase in the fixed cost and 5% is decrease in variable cost. We know that the weights w1 : w2 are 5 : 1 i.e. Fixed cost : Variable cost = 5 : 1 Hence the %age in the total cost = (13 * w1 - 5 * w2) / (w1 + w2) %change in total cost = (13 * 5 - 5 * 1) / (5 + 1) = 60/ 6 = 10% increase Good call! We see that we can use weighted averages. We already have A1, Stmnt1 gives us A2 and Stmnt2 gives us w1/w2 so we can use w1/w2 = (A2 - Avg)/(Avg - A1) and get the answer. We don't even need to calculate. Finally, I feel my effort of showing the utility of 'weighted averages' is paying off! If you were in my class, the day's candy would have been yours! 
_________________
Karishma
Veritas Prep | GMAT Instructor
My Blog
Save 10% on Veritas Prep GMAT Courses And Admissions Consulting
Enroll now. Pay later. Take advantage of Veritas Prep's flexible payment plan options.
Veritas Prep Reviews
|
|
|
|
|
|
Senior Manager
Joined: 08 Nov 2010
Posts: 435
WE 1: Business Development
Followers: 6
Kudos [?]:
25
[0], given: 161
|
Re: very hard - MGMAT [#permalink]
07 May 2011, 11:28
Karishma - can u plz post ur blogging that dealing with this weighted average system?
_________________
Find out what's new at GMAT Club - latest features and updates
|
|
|
|
|
|
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 3105
Location: Pune, India
Followers: 567
Kudos [?]:
1995
[3] , given: 92
|
Re: very hard - MGMAT [#permalink]
07 May 2011, 11:59
3
This post received
KUDOS
144144 wrote: Karishma - can u plz post ur blogging that dealing with this weighted average system? Here you go: http://www.veritasprep.com/blog/2011/03 ... -averages/http://www.veritasprep.com/blog/2011/04 ... ge-brutes/http://www.veritasprep.com/blog/2011/04 ... -mixtures/My signature gives the link to all my blog posts (they are together under the section 'Quarter Wit, Quarter Wisdom'). I have given the link for the weighted average related posts above.
_________________
Karishma
Veritas Prep | GMAT Instructor
My Blog
Save 10% on Veritas Prep GMAT Courses And Admissions Consulting
Enroll now. Pay later. Take advantage of Veritas Prep's flexible payment plan options.
Veritas Prep Reviews
|
|
|
|
|
|
Director
Joined: 03 Feb 2011
Posts: 944
Followers: 9
Kudos [?]:
137
[0], given: 121
|
Re: very hard - MGMAT [#permalink]
07 May 2011, 18:15
Ha ha yes indeed .... wow !! thanks so much ! Its a pleasure to read your posts. VeritasPrepKarishma wrote: gmat1220 wrote: Karishma Pls can you verify this solution. I think this is a weighted average problem. Combining 1) + 2) 13% increase in the fixed cost and 5% is decrease in variable cost. We know that the weights w1 : w2 are 5 : 1 i.e. Fixed cost : Variable cost = 5 : 1 Hence the %age in the total cost = (13 * w1 - 5 * w2) / (w1 + w2) %change in total cost = (13 * 5 - 5 * 1) / (5 + 1) = 60/ 6 = 10% increase Good call! We see that we can use weighted averages. We already have A1, Stmnt1 gives us A2 and Stmnt2 gives us w1/w2 so we can use w1/w2 = (A2 - Avg)/(Avg - A1) and get the answer. We don't even need to calculate. Finally, I feel my effort of showing the utility of 'weighted averages' is paying off! If you were in my class, the day's candy would have been yours! |
|
|
|
|
|
Director
Joined: 01 Feb 2011
Posts: 792
Followers: 11
Kudos [?]:
62
[0], given: 42
|
Re: very hard - MGMAT [#permalink]
07 May 2011, 20:06
TC1 = F +V
TC2 = F2+0.95V Jan
1. Not sufficient.
F2 = 0.87F
TC2 = 0.87F+0.95V
TC2/TC1 = (0.87F+0.95V)/(F+V)
2. TC= 6V
TC2 = F2+0.95V
no F2 , so not sufficient.
together we have
TC2 = 0.87F+0.95V
TC2/TC1 = (0.87F+0.95V)/(F+V) and F= 6V => sufficient.
Answer is C.
|
|
|
|
|
|
Manager
Joined: 05 Jul 2010
Posts: 207
Followers: 1
Kudos [?]:
9
[0], given: 18
|
Re: very hard - MGMAT [#permalink]
09 May 2011, 20:58
+1 for Karishma. Good info!
|
|
|
|
|
|
Manager
Status: GMAT in 4 weeks
Joined: 28 Mar 2010
Posts: 196
GPA: 3.89
Followers: 1
Kudos [?]:
22
[0], given: 25
|
Re: very hard - MGMAT [#permalink]
18 May 2011, 11:41
Its C calculations gives 10 % increase
_________________
If you liked my post, please consider a Kudos for me. Thanks!
|
|
|
|
|
|
Current Student
Joined: 26 May 2005
Posts: 575
Followers: 18
Kudos [?]:
79
[0], given: 13
|
Re: very hard - MGMAT [#permalink]
08 Jun 2011, 23:09
I would have used plugging in strategy here;
statement 2. fixed cost = 5* VC
assume VC = 20 , FC = 100 Total cost = 120
information : VC decreased 5% = 20-5% = 19
statement 1. FC increased 13% = 100+13% = 113
total new cost = 113+19 = 132
% increase over previous TC = 132-120/120 = 12/120 = 10%
|
|
|
|
|
|
Director
Status: GMAT Learner
Joined: 14 Jul 2010
Posts: 672
Followers: 21
Kudos [?]:
108
[0], given: 31
|
Re: very hard - MGMAT [#permalink]
12 Jun 2011, 03:01
|
|
|
|
|
|
Senior Manager
Joined: 20 Dec 2010
Posts: 261
Schools: UNC Duke Kellogg
Followers: 3
Kudos [?]:
18
[0], given: 4
|
Re: very hard - MGMAT [#permalink]
30 Jun 2011, 19:04
Very clever gmat1220!!...
|
|
|
|
|
|
Manager
Status: On...
Joined: 16 Jan 2011
Posts: 193
Followers: 2
Kudos [?]:
26
[0], given: 62
|
Re: very hard - MGMAT [#permalink]
10 Jul 2011, 16:16
I think most people will fall into the trap if they assume FC and VC as some values say 100,200... In this case B will be correct But this approach will work only if there is a single unknown...This is a classic example when it will not work directly There are 2 approaches 1) If you like formulas : Weighted average is the best approach as illustrated by Karishma 2) I like the lazy-man approach for DS, so I am assuming FC=x,VC=y...As per qn. y decr. by 5% So we need Increase/(x+y) x incr. by 13% as per A...But no relation b/w x and y ==> This is insufficient As per B, x=5y...But what is increase ? Combining A and B, there is a non-redundant relation and increase can be calculated So go with C and MOVE ON Choose the approach that best suites you...Also calculate values only if needed in DS. Bunuel has shown the complete steps of calculation for purely illustration...
_________________
Labor cost for typing this post >= Labor cost for pushing the Kudos Button
kudos-what-are-they-and-why-we-have-them-94812.html
|
|
|
|
|
|
Manager
Joined: 01 Jun 2011
Posts: 177
Followers: 1
Kudos [?]:
9
[0], given: 6
|
Re: very hard - MGMAT [#permalink]
13 Jul 2011, 06:00
knabi wrote: The total cost of producing item X is equal to the sum of item X's fixed cost and variable cost. If the variable cost of producing X decreased by 5% in January, by what percent did the total cost of producing item X change in January?
(1) The fixed cost of producing item X increased by 13% in January.
(2) Before the changes in January, the fixed cost of producing item X was 5 times the variable cost of producing item X.
Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
Both statements TOGETHER are sufficient, but NEITHER one ALONE is sufficient.
EACH statement ALONE is sufficient.
Statements (1) and (2) TOGETHER are NOT sufficient.
-----------
My question is, why isn't the answer B? The prompt didn't say fixed cost MUST change... haha. Less than two minutes and without any notes i must be guessed
|
|
|
|
|
|
|
Re: very hard - MGMAT
[#permalink]
13 Jul 2011, 06:00
|
|
|
|
|
|
|
|
|
|
|
close
