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

It is currently 20 May 2019, 15:46

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

Two varieties of steel, A and B, have a ratio of iron to chromium as 5

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

Hide Tags

 
Intern
Intern
avatar
Joined: 05 Aug 2014
Posts: 29
Reviews Badge
Two varieties of steel, A and B, have a ratio of iron to chromium as 5  [#permalink]

Show Tags

New post 24 May 2015, 09:03
5
27
00:00
A
B
C
D
E

Difficulty:

  55% (hard)

Question Stats:

67% (02:53) correct 33% (02:51) wrong based on 209 sessions

HideShow timer Statistics

Two varieties of steel, A and B, have a ratio of iron to chromium as 5:1 and 7:2, respectively. Steel C is produced by mixing alloys A and B at a ratio of 3:2. What is the ratio of iron to chromium in C?

(A) 17 : 73
(B) 78 : 14
(C) 45 : 30
(D) 73 : 17
(E) 4 : 9
Most Helpful Expert Reply
GMAT Tutor
avatar
S
Joined: 24 Jun 2008
Posts: 1518
Re: Two varieties of steel, A and B, have a ratio of iron to chromium as 5  [#permalink]

Show Tags

New post 24 May 2015, 09:35
5
4
In 6 parts of alloy A, 5 parts are iron, and 1 part is chromium.

In 9 parts of alloy B, 7 parts are iron and 2 parts are chromium.

First, to compare the two alloys, get the same number of parts in total - we can use 18. So we have:

In 18 parts of alloy A, 15 parts are iron and 3 are chromium.
In 18 parts of alloy B, 14 parts are iron and 4 are chromium.

So combining 3 of A with 2 of B, we'd be combining 45 and 28 parts of iron, or 73 parts of iron, with 9 and 8 of chromium, or 17 of chromium, so 73 to 17 is the answer.
_________________
GMAT Tutor in Toronto

If you are looking for online GMAT math tutoring, or if you are interested in buying my advanced Quant books and problem sets, please contact me at ianstewartgmat at gmail.com
Most Helpful Community Reply
Senior Manager
Senior Manager
avatar
B
Joined: 23 Sep 2015
Posts: 371
Location: France
GMAT 1: 690 Q47 V38
GMAT 2: 700 Q48 V38
WE: Real Estate (Mutual Funds and Brokerage)
Reviews Badge
Re: Two varieties of steel, A and B, have a ratio of iron to chromium as 5  [#permalink]

Show Tags

New post 23 Apr 2016, 04:33
2
4
Finding the weighted average of one of the two :
Iron:
In solution A iron is 5/6
In solution B iron is 7/9

The ratio for Solution C is 3:2 for A and B respectively. This means that 60% of A was used and 40% of B

To find the weight of iron in the new solution: we do the weighted average:

\(\frac{5}{6}*\frac{3}{5}+\frac{7}{9}*\frac{2}{5}\)

We get \(\frac{73}{90}\)

73 is the weight of Iron and 90 is total
_________________
General Discussion
Director
Director
User avatar
Joined: 07 Aug 2011
Posts: 520
Concentration: International Business, Technology
GMAT 1: 630 Q49 V27
GMAT ToolKit User
Re: Two varieties of steel, A and B, have a ratio of iron to chromium as 5  [#permalink]

Show Tags

New post 24 May 2015, 12:12
5
naeln wrote:
Two varieties of steel, A and B, have a ratio of iron to chromium as 5:1 and 7:2, respectively. Steel C is produced by mixing alloys A and B at a ratio of 3:2. What is the ratio of iron to chromium in C?

(A) 17 : 73
(B) 78 : 14
(C) 45 : 30
(D) 73 : 17
(E) 4 : 9

Could any one please help me understand how to go about this type of questions?

Thank you in advance.


Such questions test your knowledge on weighted average concept . Initially this technique may seem daunting but once you get familiar , you will find this technique very useful on GMAT.

Ok , so for this question we can focus on either Iron or chromium to get to the solution . i will show both ways .

in A , Iron = 5/6
in B , Iron= 7/9
resultant mixture has 3 portions of A for every 2 portions of B , so weighted average of Iron will lie closer to A than to B .
Specifically , w.Avg (Iron) in mixture will be 2 portion away from A and 3 portion away from B as shown in picture.
Attachments

gmatclub.jpg
gmatclub.jpg [ 75.74 KiB | Viewed 3574 times ]

VP
VP
avatar
P
Joined: 07 Dec 2014
Posts: 1190
Re: Two varieties of steel, A and B, have a ratio of iron to chromium as 5  [#permalink]

Show Tags

New post 08 Apr 2016, 11:50
2
iron in 3A+2B=3(5/6)+2(7/9)=73/18
chromium in 3A+2B=3(1/6)+2(2/9)=17/18
iron:chromium ratio in C=(73/18)/(17/18)=73/17
Manager
Manager
User avatar
B
Joined: 01 Jan 2018
Posts: 71
Re: Two varieties of steel, A and B, have a ratio of iron to chromium as 5  [#permalink]

Show Tags

New post 29 Sep 2018, 10:30
Combine the 2 alloys in the given ratio.
We get (3(5/6)+2(7/9))/(3(1/6)+2(2/9))=>(5/2+14/9)/(1/2+4/9)=>73/17 choice D
_________________
+1 Kudos if you find this post helpful
Intern
Intern
avatar
B
Joined: 01 Jul 2018
Posts: 21
Re: Two varieties of steel, A and B, have a ratio of iron to chromium as 5  [#permalink]

Show Tags

New post 20 Apr 2019, 01:50
1
reasoning:
we have a ratio I:C of group A and a different ratio of I:C for group B. We are given the ratio at which A and B are used to form a third group C (these are the weights). Then we are asked about the ratio of I:C of this latest group C.

what % of I do we have in A? And, how will be reflected this distribution (%) of A in group C?

(5/6)*3

what % of I do we have in I? And, how will be reflected this distribution (%) of B in group C?

(7/9)*2

Then, we apply the same reasoning for Chromium, and we end up having the following equation:


For I: (5/6)*3+(7/9)*2
For Chromium: (1/6)*3+(2/9)*2

Total Weighted Avg. ratio to get the ratio of I/C in group C:

(5/6)*3+(7/9)*2 73
------------------- = ----
(1/6)*3+(2/9)*2 17
Director
Director
User avatar
S
Joined: 17 Dec 2012
Posts: 629
Location: India
Two varieties of steel, A and B, have a ratio of iron to chromium as 5  [#permalink]

Show Tags

New post 21 Apr 2019, 03:07
naeln wrote:
Two varieties of steel, A and B, have a ratio of iron to chromium as 5:1 and 7:2, respectively. Steel C is produced by mixing alloys A and B at a ratio of 3:2. What is the ratio of iron to chromium in C?

(A) 17 : 73
(B) 78 : 14
(C) 45 : 30
(D) 73 : 17
(E) 4 : 9

Intuitive Representation
variables ---> Iron -- Chromium -- Total

Truth 1 -----> 5x -- x -- 6x
Truth 2 ------> 7y -- 2y -- 9y

Truth 3 ------> 3*5x --- 3*x -- - 18x
Truth 3 ------> 2*7y --- 2*2y --- 18y

what connections can we make?
6x=9y => x=3y/2

Iron = 3*5x+ 2*7y = 36.5y, chromium= 3*x+2*2y=8.5y
=> Iron:chromium = 73:17
_________________
Srinivasan Vaidyaraman
Sravna Test Prep
http://www.sravnatestprep.com

Holistic and Systematic Approach
Intern
Intern
avatar
B
Joined: 15 Aug 2014
Posts: 3
CAT Tests
Re: Two varieties of steel, A and B, have a ratio of iron to chromium as 5  [#permalink]

Show Tags

New post 21 Apr 2019, 03:45
Using Alligation to knock out this one :

Lets take the Iron part :

[5][/6] [7][/9]

x
3 2

This simplifies to : [7-9x][/6x-5] = [9][/4]
which boils down to x = [73][/90]

But remember we started with part to the whole so the above is the expression for Iron to whole ( in C)
Therefore the desired ratio will be : [73][/90-73]= [73][/17], which is D
GMAT Club Bot
Re: Two varieties of steel, A and B, have a ratio of iron to chromium as 5   [#permalink] 21 Apr 2019, 03:45
Display posts from previous: Sort by

Two varieties of steel, A and B, have a ratio of iron to chromium as 5

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


Copyright

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®.