Help requested for mixture question

Expert replies

cyrusthegreat: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Sat Jan 30, 2010 8:31 pm

by cyrusthegreat » Tue Apr 13, 2010 2:30 pm

An alloy contains copper and zinc in the ratio of 5:3 and another contains copper and tin in the ratio of 8:5. If equal weights of the two are melted together to form a new alloy, find the weight of tin per kg in the new alloy.

A. 42/126 Kg

B. 5/28 Kg

C. 5/13 Kg

D. 5/26Kg

E. None of these

I came up with 25/129 and so chose e but it was incorrect.

This is how I got to my answer:

40c:24z 40c:25t 40+24+40+25 = 129 t=25 25/129 equals the proportion of a kg that is tin if all parts are melted down and recast as a new alloy.

Anyone know where I went wrong?

Thanks in advance

Like this post

Source: Beat The GMAT — Problem Solving | Tue Apr 13, 2010 2:30 pm

kevincanspain: GMAT Instructor; Posts: 613; Joined: Thu Mar 22, 2007 6:17 amFollowed by: 64 members; Location: madrid; Thanked: 171 times; GMAT Score:790

by kevincanspain » Tue Apr 13, 2010 2:45 pm

Alloy 1
Copper = 5x Zinc =3x
Total 8x

Alloy 2
Copper = 8y, Tin =5y
Total 13y =8x (the weights of the alloys are equal)

Total weight 26y, of which 5y is tin: Answer: D

You mistakenly equated the weights of copper in the two alloys

Kevin Armstrong
GMAT Instructor
Gmatclasses
Madrid

Like this post

cyrusthegreat: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Sat Jan 30, 2010 8:31 pm

by cyrusthegreat » Tue Apr 13, 2010 3:25 pm

Thanks Kevin. I have another one that I'd appreciate some help with as well:

Two liquids are mixed in the proportion of 3:2 and the mixture is sold at $11 per litre at a 10% profit. If the 1st liquid costs $2 more per litre than the second, what does it cost per litre?

A. $11

B. $10.80

C. $10.40

D. $11.75

Thanks in advance

Like this post

cyrusthegreat: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Sat Jan 30, 2010 8:31 pm

by cyrusthegreat » Tue Apr 13, 2010 3:27 pm

Does anyone know at what level of difficulty these 2 questions would be considered?

Like this post

dxgamez: Senior | Next Rank: 100 Posts; Posts: 65; Joined: Wed Nov 25, 2009 6:33 pm; Thanked: 3 times

by dxgamez » Tue Apr 13, 2010 5:01 pm

Mixture original price would be at $10, as it is sold at 10% profit, which costs $11.

Let cost of 1st liquid be $x per litre and cost of 2nd liquid be $y per litre

$x = $y + $2

(3/5)*(x) + (2/5)*(y) = $10 --> everything is $ per litre and the proportions are stated in the qn.

sub x = y + 2 into above

(3/5)*(y+2) + (2/5)*y = 10 and multiplying both sides by 5 gives:-

3(y+2) + 2y = 50
y = 44/5 = $8.8 per litre

thus, x = $8.8 + $2 = $10.80...Answer is B.

Kevin, your take pls, for a clearer explanation?

Like this post

cyrusthegreat: Junior | Next Rank: 30 Posts; Posts: 11; Joined: Sat Jan 30, 2010 8:31 pm

by cyrusthegreat » Tue Apr 13, 2010 6:30 pm

Thanks dxgames. Anyone know the difficulty level of these questions?

Like this post

eaakbari: Master | Next Rank: 500 Posts; Posts: 435; Joined: Mon Mar 15, 2010 6:15 amFollowed by: 1 member; Thanked: 32 times

by eaakbari » Wed Apr 14, 2010 10:41 am

kevincanspain wrote:Alloy 1
Copper = 5x Zinc =3x
Total 8x

Alloy 2
Copper = 8y, Tin =5y
Total 13y =8x (the weights of the alloys are equal)

Total weight 26y, of which 5y is tin: Answer: D

You mistakenly equated the weights of copper in the two alloys

Hey Kevin

Dont you mean 21 y in the bold part as 13 + 8 = 21
I got the answer as 5/21

Whether you think you can or can't, you're right.
- Henry Ford

Like this post

harshavardhanc: Legendary Member; Posts: 526; Joined: Sat Feb 21, 2009 11:47 pm; Location: India; Thanked: 68 times; GMAT Score:680

by harshavardhanc » Wed Apr 14, 2010 11:09 am

eaakbari wrote:
kevincanspain wrote:Alloy 1
Copper = 5x Zinc =3x
Total 8x

Alloy 2
Copper = 8y, Tin =5y
Total 13y =8x (the weights of the alloys are equal)

Total weight 26y, of which 5y is tin: Answer: D

You mistakenly equated the weights of copper in the two alloys
Hey Kevin

Dont you mean 21 y in the bold part as 13 + 8 = 21
I got the answer as 5/21

it will be 5/26.

See it this way : you take 1 Kg each of both the mixtures.

We have (5/13) * 1 kg of tin in 2 Kgs of the total mixture. so tin is (5/26) per Kg.

Regards,
Harsha

Like this post

Post new topic Post Reply

• Page 1 of 1

GMAT Course Reviews

560 reviews

1168 reviews

431 reviews

359 reviews

147 reviews

5/5

5 Star (560 Reviews)

"Target Test Prep is the closest to the official version of the GMAT exam, about 99% accuracy in terms of the quality and quantity of information. The course has excellently created singular sets of focused lessons and tests for every possible topic that one could come across in the official GMAT exam."

"The TTP course maximizes the efficiency of the time you spend studying. It will take time and effort but I could almost guarantee that if you complete the course exactly as it is laid out you will get an amazing score. They also have a very responsive team willing to help with any questions you might have."

"TTP has two things that I think no other test prep company offers: A teaching approach that reinforces understanding and an attitude that will give you the mental preparedness needed to succeed on the test. TTP gives you a deep understanding of the concept you need to know while teaching you how to think."

Write a Review