Events & Promotions
| Last visit was: 20 Sep 2026, 14:19 |
It is currently 20 Sep 2026, 14:20 |
|
|
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
Track
Your Progress
Practice
Pays
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Sep 1810:00 AM IST
-11:00 PM IST
Start your journey with a fully customized action plan and work with a dedicated mentor to achieve a 735+ score.
Sep 2003:30 AM EDT
-04:30 AM EDT
Looking for your GMAT motivation to break through the score plateau? Pragati improved her score by massive 160 points with strategic guidance and hard-work! Find out how personalized mentorship and a strong mindset can turn GMAT struggles into success.
Sep 2107:00 PM EDT
-10:00 PM EDT
Boost your GMAT score in less than one month in a live online class + 6 months access to TTP OnDemand video courses included!
Sep 2312:30 AM EDT
-01:30 AM EDT
Learn how Keshav, a Chartered Accountant, scored an impressive 705 on GMAT in just 30 days with GMATWhiz's expert guidance. In this video, he shares preparation tips and strategies that worked for him, including the mock, time management, and more
Sep 2601:00 PM EDT
-04:00 PM EDT
Top scores are possible when you enroll in a powerful GMAT course, taught live online + 6 months access to TTP OnDemand video courses included. Class starts Saturdays Sept. 26, 2026 - Dec. 19, 2026, 1:00pm-4:00pm ES
Sep 2606:00 PM PDT
-07:00 PM PDT
Free- full-length test + 15 concept videos + 150+ short videos + study plan!
22 Sep 2020, 04:00
Kudos
Bookmarks
D
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
45%
(medium)
Question Stats:
73% (02:38) correct
27%
(02:38)
wrong
based on 346
sessions
History
Date
Time
Result
Not Attempted Yet
A golden brick of 0.950 purity weighs 6300 grams. What amount of pure copper should be added to lower its purity to 0.900?
A. 250 grams
B. 300 grams
C. 320 grams
D. 350 grams
E. 370 grams
A. 250 grams
B. 300 grams
C. 320 grams
D. 350 grams
E. 370 grams
22 Sep 2020, 04:36
Kudos
Bookmarks
6300 gms of Gold contains 0.95 or 95% Gold.
Amount of gold = \(\frac{95}{100} * 6300 = 5985\) gms
Let x gms of pure copper be added, so that the percentage of gold becomes 0.9 or 90%
Total Weight = (6300 + x) gms
By the rule of percentages, \(\frac{Percentage}{100} * Total = Portion\)
\(\frac{90}{100} * (6300 + x) = 5985\)
\(6300 \space + \space x = \frac{100}{90} * 5985\)
6300 + x = 6650
x = 6650 - 6300 = 350 gms
Option D
Arun Kumar
Amount of gold = \(\frac{95}{100} * 6300 = 5985\) gms
Let x gms of pure copper be added, so that the percentage of gold becomes 0.9 or 90%
Total Weight = (6300 + x) gms
By the rule of percentages, \(\frac{Percentage}{100} * Total = Portion\)
\(\frac{90}{100} * (6300 + x) = 5985\)
\(6300 \space + \space x = \frac{100}{90} * 5985\)
6300 + x = 6650
x = 6650 - 6300 = 350 gms
Option D
Arun Kumar
General Discussion
23 Sep 2020, 09:00
Kudos
Bookmarks
6300g corresponds to 0.95,
'x' g corresponds to 0.90
hence x = (6300*0.9)/0.95 = 5968 (approx)
Hence an addition of 6300-5968 is resulting in the lowering of its purity. Which is 350g.
Option [D]
'x' g corresponds to 0.90
hence x = (6300*0.9)/0.95 = 5968 (approx)
Hence an addition of 6300-5968 is resulting in the lowering of its purity. Which is 350g.
Option [D]
Hi VeritasKarishma
I tried to solve above problem using weighted average formula but the answer I got is not even in the option and off by 2600gms (approx).
Then I solved it using concentration formula since the amount of gold remains the same and its only the volume/weight of the final product that is changing. Then I got the correct answer.
Could we even solve this problem using weighted average? If yes, how? Please help. I am trying to get my head around weighted average and every now and then I get stuck in such a problem.
Here is how I substituted values in both the formulae :
1: weighted average
W(g)/W(c) = (A(copper) - A(avg)/A(gold)-A(avg))
5985/w(c) = (1-0.9)/(0.95-0.9) Note: brick is 95% gold so W(g) = 6300 * 0.95 = 5985gms
W(c) = 2995.5 gms obviously incorrect!!
2: Concentration way
ViCi = VfCf
(0.95)6300 = Vf(0.9)
Vf = 6650
amount of copper used = 6650 - 6300 = 350gms correct.
Edit 1:
Hi VeritasKarishma
I found my mistake. I should have considered ratio of mixtures instead of ratio of two components. duh!!
0%|------------------90%----|95%
(100%Copper) (Desired) (given 95% pure gold bar = 6300gms)
w1/w2 = 5/90 = 1/18
since w2 is 6300 gms
w1 = (1/18) * 6300 = 350gms!!
I tried to solve above problem using weighted average formula but the answer I got is not even in the option and off by 2600gms (approx).
Then I solved it using concentration formula since the amount of gold remains the same and its only the volume/weight of the final product that is changing. Then I got the correct answer.
Could we even solve this problem using weighted average? If yes, how? Please help. I am trying to get my head around weighted average and every now and then I get stuck in such a problem.
Here is how I substituted values in both the formulae :
1: weighted average
W(g)/W(c) = (A(copper) - A(avg)/A(gold)-A(avg))
5985/w(c) = (1-0.9)/(0.95-0.9) Note: brick is 95% gold so W(g) = 6300 * 0.95 = 5985gms
W(c) = 2995.5 gms obviously incorrect!!
2: Concentration way
ViCi = VfCf
(0.95)6300 = Vf(0.9)
Vf = 6650
amount of copper used = 6650 - 6300 = 350gms correct.
Edit 1:
Hi VeritasKarishma
I found my mistake. I should have considered ratio of mixtures instead of ratio of two components. duh!!
0%|------------------90%----|95%
(100%Copper) (Desired) (given 95% pure gold bar = 6300gms)
w1/w2 = 5/90 = 1/18
since w2 is 6300 gms
w1 = (1/18) * 6300 = 350gms!!
Attachments
tenor.gif [ 374.37 KiB | Viewed 4913 times ]
