GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 16 Jul 2018, 16:43

Close

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
Your Progress

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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

An alloy contains tin and copper in the ratio of 4:5 . If tin has 20%

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Expert Post
3 KUDOS received
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 47019
An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

Show Tags

New post 07 Feb 2014, 04:31
3
6
00:00
A
B
C
D
E

Difficulty:

  45% (medium)

Question Stats:

65% (01:23) correct 35% (01:48) wrong based on 222 sessions

HideShow timer Statistics

An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% impurity and copper has 58% , what is the avg impurity percentage ?

A. 20%

B. 41.1%

C. 35%

D. 38%

E. 43.1%

_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

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. ,11 Mixed Questions, 12 Fresh Meat

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., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 47019
An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

Show Tags

New post 07 Feb 2014, 11:22
2 KUDOS received
SVP
SVP
User avatar
Status: The Best Or Nothing
Joined: 27 Dec 2012
Posts: 1837
Location: India
Concentration: General Management, Technology
WE: Information Technology (Computer Software)
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

Show Tags

New post 04 Mar 2014, 01:51
2
Impurity in tin = 20% of 4/9 = 80/900
Impurity in Cu = 58% of 5/9 = 290/900

Total Impurity = 380/900. Percent = 380/9 = 41.2
Answer = B
_________________

Kindly press "+1 Kudos" to appreciate :)

Expert Post
SVP
SVP
avatar
B
Joined: 06 Nov 2014
Posts: 1888
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

Show Tags

New post 29 Mar 2015, 07:52
Bunuel wrote:
aimlockfire1 wrote:
An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% impurity and copper has 58% , what is the avg impurity percentage ?

a) 20%

b) 41.1%

c) 35%

d) 38%

e) 43.1%


(4*0.2 + 5*0.58)/(4+5) = ~41%.

Answer: B.


Tin and copper are in ratio of 4:5. So let total mixture be 4+5 = 9.
So, tin = 4 and copper = 5.
Now, tin has 20% impurity = 20% * 4 = 0.8
Also, copper has 58% impurity = 58% * 5 = 2.9
Average = (0.8 + 2.9)/(4+5)
= 3.7/9
= 0.411
= 41.1%

Hence option (B).

--
Optimus Prep's GMAT On Demand course for only $299 covers all verbal and quant. concepts in detail. Visit the following link to get your 7 days free trial account: http://www.optimus-prep.com/gmat-on-demand-course
Intern
Intern
avatar
Joined: 09 Oct 2011
Posts: 23
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

Show Tags

New post 18 May 2015, 10:18
An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% impurity and copper has 58% , what is the avg impurity percentage ?

a) 20%

b) 41.1%

c) 35%

d) 38%

e) 43.1%



The problem is on ratio / Proportion but look closely it can be solved with weighted average concept

(4*0.2 + 5*0.58)/(4+5) = ~41%.

Answer: B.
Intern
Intern
avatar
Joined: 21 May 2012
Posts: 2
Premium Member
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

Show Tags

New post 18 May 2015, 10:46
Its a 10sec Question.
Because tin:Copper is in the ratio 4:5, there is more of Copper and hence more impurities from Copper in the final alloy. Since Copper has 58% impurities, the overall average should be closer to 58%, which narrows down the options to B or E. Since T:C is close to 1 (4:5), we want to pick the option closer to the middle but more towards C, which is 42%. Hence option B
Director
Director
User avatar
P
Joined: 05 Mar 2015
Posts: 980
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

Show Tags

New post 26 May 2016, 19:19
Bunuel wrote:
aimlockfire1 wrote:
An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% impurity and copper has 58% , what is the avg impurity percentage ?

a) 20%

b) 41.1%

c) 35%

d) 38%

e) 43.1%


(4*0.2 + 5*0.58)/(4+5) = ~41%.

Answer: B.

Can be done with weighted avg. formula
w1/w2=(a2-avg)/(avg-a1)
4/5=(58-x)/(x-20)
x=41.1
Ans B
Intern
Intern
User avatar
B
Joined: 01 Jan 2016
Posts: 21
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

Show Tags

New post 09 May 2018, 01:21
Bunuel wrote:
An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% impurity and copper has 58% , what is the avg impurity percentage ?

A. 20%

B. 41.1%

C. 35%

D. 38%

E. 43.1%


(4*0.2 + 5*0.58)/(4+5) = ~41%.

Answer: B.


Perhaps this is extremely obvious, but how are you able to "see" the last operation so precisely. I.e. does it not require no division by a decimal without a calculator to determine the ~41%? Best regards.
Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 47019
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

Show Tags

New post 09 May 2018, 01:28
GMAT2645 wrote:
Bunuel wrote:
An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% impurity and copper has 58% , what is the avg impurity percentage ?

A. 20%

B. 41.1%

C. 35%

D. 38%

E. 43.1%


(4*0.2 + 5*0.58)/(4+5) = ~41%.

Answer: B.


Perhaps this is extremely obvious, but how are you able to "see" the last operation so precisely. I.e. does it not require no division by a decimal without a calculator to determine the ~41%? Best regards.


\(\frac{(4*0.2 + 5*0.58)}{(4+5)} = \frac{0.8+2.9}{9}= \frac{3.7}{9}\).

3.6/9 = 0.4, so 3.7/9 will be a bit larger.
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

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. ,11 Mixed Questions, 12 Fresh Meat

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., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Senior Manager
Senior Manager
User avatar
G
Joined: 14 Oct 2017
Posts: 250
GMAT 1: 710 Q44 V41
CAT Tests
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

Show Tags

New post 09 May 2018, 05:38
We can also transition the fraction to percent by recognizing that a fraction with denominator of 9 can be multiplied by 11 to generate an approximation.

\(\frac{3.7}{9}*11 = \frac{40.7}{99}\). As we divide only by 99 and not by 100 the value in percent must be slightly higher so 41,1% is the only reasonable answer.
_________________

My goal: 700 GMAT score - REACHED :-) | My debrief - first attempt 710 (Q44,V41,IR7)

If I could help you with my answer, consider giving me Kudos

Expert Post
Target Test Prep Representative
User avatar
G
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 2918
Location: United States (CA)
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

Show Tags

New post 10 May 2018, 10:33
Bunuel wrote:
An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% impurity and copper has 58% , what is the avg impurity percentage ?

A. 20%

B. 41.1%

C. 35%

D. 38%

E. 43.1%


Let’s re-express the ratio of tin to copper as 4x : 5x. The average impurity is:

[4x(0.2) + 5x(0.58)]/9x = (0.8x + 2.9x)/9x = 3.7/9 = 0.411 = 41.1%.

Answer: B
_________________

Scott Woodbury-Stewart
Founder and CEO

GMAT Quant Self-Study Course
500+ lessons 3000+ practice problems 800+ HD solutions

Intern
Intern
User avatar
B
Joined: 01 Jan 2016
Posts: 21
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

Show Tags

New post 16 May 2018, 18:37
Bunuel wrote:
An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% impurity and copper has 58% , what is the avg impurity percentage ?

A. 20%

B. 41.1%

C. 35%

D. 38%

E. 43.1%


(4*0.2 + 5*0.58)/(4+5) = ~41%.

Answer: B.


Are you completing the (4*0.2 + 5*0.58)/(4+5) = ~41% calculation in your head? Thank you.
Intern
Intern
User avatar
B
Joined: 01 Jan 2016
Posts: 21
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

Show Tags

New post 16 May 2018, 18:42
ScottTargetTestPrep wrote:
Bunuel wrote:
An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% impurity and copper has 58% , what is the avg impurity percentage ?

A. 20%

B. 41.1%

C. 35%

D. 38%

E. 43.1%


Let’s re-express the ratio of tin to copper as 4x : 5x. The average impurity is:

[4x(0.2) + 5x(0.58)]/9x = (0.8x + 2.9x)/9x = 3.7/9 = 0.411 = 41.1%.

Answer: B


When it comes to the simple arithmetic such as "5x(0.58) = 2.9x" or "3.7/9 = 0.411" what shortcuts are you using to compute these calculations? Thank you.
Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 47019
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]

Show Tags

New post 16 May 2018, 21:49
GMAT2645 wrote:
Bunuel wrote:
An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% impurity and copper has 58% , what is the avg impurity percentage ?

A. 20%

B. 41.1%

C. 35%

D. 38%

E. 43.1%


(4*0.2 + 5*0.58)/(4+5) = ~41%.

Answer: B.


Are you completing the (4*0.2 + 5*0.58)/(4+5) = ~41% calculation in your head? Thank you.


Check this: https://gmatclub.com/forum/an-alloy-con ... l#p2058527
_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

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. ,11 Mixed Questions, 12 Fresh Meat

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., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20%   [#permalink] 16 May 2018, 21:49
Display posts from previous: Sort by

An alloy contains tin and copper in the ratio of 4:5 . If tin has 20%

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  

Events & Promotions

PREV
NEXT


GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.