NEW HERE? LEARN MORE
closeclose
Last visit was: 24 Apr 2024, 21:49 It is currently 24 Apr 2024, 21:49
Decision Tracker
My Rewards
New posts
New comers' posts

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.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel

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

SORT BY:
Date
Kudos
Tags:
Find Similar Topics 
Show Tags
Hide Tags
User avatar
L
Bunuel
Math Expert
Joined: 02 Sep 2009
Posts: 92900
Own Kudos [?]: 618844 [11]
Given Kudos: 81588
Send PM
CAT Tests Forum Quiz Mode
An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink] New post   07 Feb 2014, 04:31
3
Kudos
8
Bookmarks
Expert Reply
00:00
A
B
C
D
E

Difficulty:

45% (medium)

Question Stats:

67% (01:50) correct 33% (02:08) wrong based on 322 sessions
Hide Show 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%
ShowHide Answer
Official Answer
B
User avatar
L
Bunuel
Math Expert
Joined: 02 Sep 2009
Posts: 92900
Own Kudos [?]: 618844 [2]
Given Kudos: 81588
Send PM
CAT Tests Forum Quiz Mode
An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink] New post   07 Feb 2014, 11:22
1
Kudos
1
Bookmarks
Expert Reply
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.
avatar
PareshGmat
SVP
SVP
Joined: 27 Dec 2012
Status:The Best Or Nothing
Posts: 1562
Own Kudos [?]: 7208 [3]
Given Kudos: 193
Location: India
Concentration: General Management, Technology
WE:Information Technology (Computer Software)
Send PM
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink] New post   04 Mar 2014, 01:51
3
Kudos
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
avatar
B
OptimusPrepJanielle
SVP
SVP
Joined: 06 Nov 2014
Posts: 1798
Own Kudos [?]: 1367 [0]
Given Kudos: 23
Send PM
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink] New post   29 Mar 2015, 07:52
Expert Reply
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: https://www.optimus-prep.com/gmat-on-demand-course
avatar
vijayshree
Intern
Intern
Joined: 09 Oct 2011
Posts: 18
Own Kudos [?]: 76 [1]
Given Kudos: 9
Send PM
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink] New post   18 May 2015, 10:18
1
Kudos
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.
avatar
BD0176
Intern
Intern
Joined: 21 May 2012
Posts: 1
Own Kudos [?]: [0]
Given Kudos: 7
Send PM
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink] 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
User avatar
L
rohit8865
Director
Director
Joined: 05 Mar 2015
Posts: 852
Own Kudos [?]: 860 [0]
Given Kudos: 45
Send PM
Reviews Badge
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink] 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
avatar
B
GMAT2645
Intern
Intern
Joined: 01 Jan 2016
Posts: 20
Own Kudos [?]: 3 [0]
Given Kudos: 24
Send PM
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink] 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.
User avatar
L
Bunuel
Math Expert
Joined: 02 Sep 2009
Posts: 92900
Own Kudos [?]: 618844 [0]
Given Kudos: 81588
Send PM
CAT Tests Forum Quiz Mode
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink] New post   09 May 2018, 01:28
Expert Reply
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.
User avatar
G
Masterscorp
Manager
Manager
Joined: 14 Oct 2017
Posts: 192
Own Kudos [?]: 271 [0]
Given Kudos: 385
GMAT 1: 710 Q44 V41
Send PM
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink] 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.
User avatar
L
ScottTargetTestPrep
Target Test Prep Representative
Joined: 14 Oct 2015
Status:Founder & CEO
Affiliations: Target Test Prep
Posts: 18756
Own Kudos [?]: 22049 [0]
Given Kudos: 283
Location: United States (CA)
Send PM
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink] New post   10 May 2018, 10:33
Expert Reply
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
avatar
B
GMAT2645
Intern
Intern
Joined: 01 Jan 2016
Posts: 20
Own Kudos [?]: 3 [0]
Given Kudos: 24
Send PM
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink] 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.
avatar
B
GMAT2645
Intern
Intern
Joined: 01 Jan 2016
Posts: 20
Own Kudos [?]: 3 [0]
Given Kudos: 24
Send PM
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink] 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.
User avatar
L
Bunuel
Math Expert
Joined: 02 Sep 2009
Posts: 92900
Own Kudos [?]: 618844 [0]
Given Kudos: 81588
Send PM
CAT Tests Forum Quiz Mode
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink] New post   16 May 2018, 21:49
Expert Reply
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
User avatar
bumpbot
Non-Human User
Joined: 09 Sep 2013
Posts: 32657
Own Kudos [?]: 821 [0]
Given Kudos: 0
Send PM
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink] New post   13 Apr 2021, 03:15
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.
GMAT Club Bot
gmatclubot
Re: An alloy contains tin and copper in the ratio of 4:5 . If tin has 20% [#permalink]
13 Apr 2021, 03:15
Moderators:
Bunuel
Math Expert
92900 posts
yashikaaggarwal
Senior Moderator - Masters Forum
3137 posts

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne
Main navigation
GMAT Resources
Partners
MBA Resources
www.gmac.com|www.mba.com | | GMAT Club Rules | Terms and Conditions