A bar of gold with dimensions 12 inches by 18 inches by 15

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BTGmoderatorDC: Moderator; Posts: 7187; Joined: Thu Sep 07, 2017 4:43 pm; Followed by:23 members

A bar of gold with dimensions 12 inches by 18 inches by 15

by BTGmoderatorDC » Wed Nov 22, 2017 1:59 pm

A bar of gold with dimensions 12 inches by 18 inches by 15 inches is melted down and re-formed into a bar of different dimensions. All of the following are possible dimensions of the new gold bar EXCEPT:

A. 10 inches by 15 inches by 22 inches

B. 12 inches by 10 inches by 27 inches

C. 6 inches by 18 inches by 30 inches

D.24 inches by 27 inches by 5 inches

E. 9 inches by 24 inches by 15 inches

Can some experts find the best Option?

OA A

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Source: Beat The GMAT — Problem Solving | Wed Nov 22, 2017 1:59 pm

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by Jay@ManhattanReview » Wed Nov 22, 2017 8:38 pm

lheiannie07 wrote:A bar of gold with dimensions 12 inches by 18 inches by 15 inches is melted down and re-formed into a bar of different dimensions. All of the following are possible dimensions of the new gold bar EXCEPT:

A. 10 inches by 15 inches by 22 inches

B. 12 inches by 10 inches by 27 inches

C. 6 inches by 18 inches by 30 inches

D.24 inches by 27 inches by 5 inches

E. 9 inches by 24 inches by 15 inches

Can some experts find the best Option?

OA A

The volume of the reformed bar must be equal to the original bar.

Volume of the original bar = 12 * 18 * 15; let's factorize it into prime factors.

12 * 18 * 15 = (2^2 * 3) * (2 * 3^2) * (3 * 5) = 2^3 * 3^4 * 5

The option that does not have prime factors of their volume = 2^3 * 3^4 * 5 is the correct answer.

We see that one of the dimensions of option A is 22 inches; this will give a prime factor 11, which is not there is the volume of the original bar, thus, it is the correct answer.

The correct answer: A

Hope this helps!

-Jay
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EconomistGMATTutor: GMAT Instructor; Posts: 555; Joined: Wed Oct 04, 2017 4:18 pm; Thanked: 180 times; Followed by:12 members

A bar of gold with dimensions 12 inches by 18 inches by 15

by EconomistGMATTutor » Thu Nov 23, 2017 12:39 pm

A bar of gold with dimensions 12 inches by 18 inches by 15 inches is melted down and re-formed into a bar of different dimensions. All of the following are possible dimensions of the new gold bar EXCEPT:

A. 10 inches by 15 inches by 22 inches

B. 12 inches by 10 inches by 27 inches

C. 6 inches by 18 inches by 30 inches

D.24 inches by 27 inches by 5 inches

E. 9 inches by 24 inches by 15 inches

Can some experts find the best Option?

OA A

Hi lheiannie07,
Let's take a look at your question.

Volume of the bar of gold can be represented as:
$$=12\times18\times15inches^3$$

Write it as a product of prime factors.
$$=2\times2\times3\times2\times3\times3\times3\times5\ inches^3$$
$$=2^3\times3^4\times5\ inches^3$$

Let's now write the given options as a product of their prime factors and check which one of these is different from the volume of gold bar.
Option A:
10 inches by 15 inches by 22 inches
$$=10\times15\times22\ inches^3$$
$$=2\times5\times3\times5\times2\times11\ inches^3$$
$$=2^2\times3\times5^2\times11\ inches^3$$

This does not represent the volume of the gold bar as it is different from $$2^3\times3^4\times5\ inches^3$$ .

Therefore, Option A is correct.

Hope it helps.
I am available if you'd like any follow up.

GMAT Prep From The Economist
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Our average student improves 98 points.

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by [email protected] » Fri Nov 24, 2017 10:31 am

Hi lheiannie07,

We're told that a bar of gold with dimensions 12 inches by 18 inches by 15 inches is melted down and re-formed into a bar of different dimensions. We're also told that 4 of the 5 answers choices ARE possible dimensions of the new gold bar. We're asked to find the one that's NOT. We can actually use the answer choices 'against' the prompt and TEST THE ANSWERS.

To start, this question involves the VOLUME of the gold bar - although we don't actually have to calculate the entire volume. Notice the dimensions (12 by 18 by 15)...

Answer A: 10 by 15 by 22

This Answer includes a 15 (the same as the original bar had), so we can 'ignore' those 15s and focus on what's left: (10 by 22) vs. (12 by 18)....
(10 by 22) = 220
(12 by 18) = 216
These are NOT the same results. The volume of Answer A would be BIGGER than the volume of the original bar, so this result is NOT possible and Answer A must be the answer.

Final Answer: A

GMAT assassins aren't born, they're made,
Rich

Contact Rich at [email protected]

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BTGmoderatorDC: Moderator; Posts: 7187; Joined: Thu Sep 07, 2017 4:43 pm; Followed by:23 members

by BTGmoderatorDC » Wed Jan 17, 2018 9:48 pm

EconomistGMATTutor wrote:
A bar of gold with dimensions 12 inches by 18 inches by 15 inches is melted down and re-formed into a bar of different dimensions. All of the following are possible dimensions of the new gold bar EXCEPT:

A. 10 inches by 15 inches by 22 inches

B. 12 inches by 10 inches by 27 inches

C. 6 inches by 18 inches by 30 inches

D.24 inches by 27 inches by 5 inches

E. 9 inches by 24 inches by 15 inches

Can some experts find the best Option?

OA A
Hi lheiannie07,
Let's take a look at your question.

Volume of the bar of gold can be represented as:
$$=12\times18\times15inches^3$$

Write it as a product of prime factors.
$$=2\times2\times3\times2\times3\times3\times3\times5\ inches^3$$
$$=2^3\times3^4\times5\ inches^3$$

Let's now write the given options as a product of their prime factors and check which one of these is different from the volume of gold bar.
Option A:
10 inches by 15 inches by 22 inches
$$=10\times15\times22\ inches^3$$
$$=2\times5\times3\times5\times2\times11\ inches^3$$
$$=2^2\times3\times5^2\times11\ inches^3$$

This does not represent the volume of the gold bar as it is different from $$2^3\times3^4\times5\ inches^3$$ .

Therefore, Option A is correct.

Hope it helps.
I am available if you'd like any follow up.

Thanks a lot!

Quote

BTGmoderatorDC: Moderator; Posts: 7187; Joined: Thu Sep 07, 2017 4:43 pm; Followed by:23 members

by BTGmoderatorDC » Wed Jan 17, 2018 9:48 pm

Jay@ManhattanReview wrote:
lheiannie07 wrote:A bar of gold with dimensions 12 inches by 18 inches by 15 inches is melted down and re-formed into a bar of different dimensions. All of the following are possible dimensions of the new gold bar EXCEPT:

A. 10 inches by 15 inches by 22 inches

B. 12 inches by 10 inches by 27 inches

C. 6 inches by 18 inches by 30 inches

D.24 inches by 27 inches by 5 inches

E. 9 inches by 24 inches by 15 inches

Can some experts find the best Option?

OA A
The volume of the reformed bar must be equal to the original bar.

Volume of the original bar = 12 * 18 * 15; let's factorize it into prime factors.

12 * 18 * 15 = (2^2 * 3) * (2 * 3^2) * (3 * 5) = 2^3 * 3^4 * 5

The option that does not have prime factors of their volume = 2^3 * 3^4 * 5 is the correct answer.

We see that one of the dimensions of option A is 22 inches; this will give a prime factor 11, which is not there is the volume of the original bar, thus, it is the correct answer.

The correct answer: A

Hope this helps!

-Jay
_________________
Manhattan Review GMAT Prep

Locations: New York | Singapore | Doha | Lausanne | and many more...

Schedule your free consultation with an experienced GMAT Prep Advisor! Click here.

Thanks a lot!

Quote

BTGmoderatorDC: Moderator; Posts: 7187; Joined: Thu Sep 07, 2017 4:43 pm; Followed by:23 members

by BTGmoderatorDC » Wed Jan 17, 2018 9:57 pm

[email protected] wrote:Hi lheiannie07,

We're told that a bar of gold with dimensions 12 inches by 18 inches by 15 inches is melted down and re-formed into a bar of different dimensions. We're also told that 4 of the 5 answers choices ARE possible dimensions of the new gold bar. We're asked to find the one that's NOT. We can actually use the answer choices 'against' the prompt and TEST THE ANSWERS.

To start, this question involves the VOLUME of the gold bar - although we don't actually have to calculate the entire volume. Notice the dimensions (12 by 18 by 15)...

Answer A: 10 by 15 by 22

This Answer includes a 15 (the same as the original bar had), so we can 'ignore' those 15s and focus on what's left: (10 by 22) vs. (12 by 18)....
(10 by 22) = 220
(12 by 18) = 216
These are NOT the same results. The volume of Answer A would be BIGGER than the volume of the original bar, so this result is NOT possible and Answer A must be the answer.

Final Answer: A

GMAT assassins aren't born, they're made,
Rich

Thanks a lot!

Quote

regor60: Master | Next Rank: 500 Posts; Posts: 416; Joined: Thu Oct 15, 2009 11:52 am; Thanked: 27 times

by regor60 » Thu Jan 18, 2018 11:53 am

lheiannie07 wrote:A bar of gold with dimensions 12 inches by 18 inches by 15 inches is melted down and re-formed into a bar of different dimensions. All of the following are possible dimensions of the new gold bar EXCEPT:

A. 10 inches by 15 inches by 22 inches

B. 12 inches by 10 inches by 27 inches

C. 6 inches by 18 inches by 30 inches

D.24 inches by 27 inches by 5 inches

E. 9 inches by 24 inches by 15 inches

Can some experts find the best Option?

OA A

Following on based on the factorization, you can see there is only 5 represented.

Inspecting the choices indicates that all the choices except A have just one 5 as a factor and that A has two factors of 5

Quote

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Scott@TargetTestPrep: GMAT Instructor; Posts: 8086; Joined: Sat Apr 25, 2015 10:56 am; Location: Los Angeles, CA; Thanked: 43 times; Followed by:29 members

by Scott@TargetTestPrep » Sat Jan 20, 2018 6:16 am

lheiannie07 wrote:A bar of gold with dimensions 12 inches by 18 inches by 15 inches is melted down and re-formed into a bar of different dimensions. All of the following are possible dimensions of the new gold bar EXCEPT:

A. 10 inches by 15 inches by 22 inches

B. 12 inches by 10 inches by 27 inches

C. 6 inches by 18 inches by 30 inches

D.24 inches by 27 inches by 5 inches

E. 9 inches by 24 inches by 15 inches

The key to solving this problem is to notice that when we melt and re-form the gold bar, the volume of the re-formed gold bar will be the same as the original gold bar. Therefore, we must compare the volumes of the answer choices with the volume of the given gold bar.

A helpful way to solve this problem is to recognize that we can factor the answer choices to determine any difference between the factors of the dimensions in those choices and the given dimensions of 12 by 18 by 15. The original bar's dimensions factor to 2^3 x 3^4 x 5^1. In scanning the answer choices, we see that answer choice A has dimensions of 10 by 15 by 22. Thus, those dimensions contain a factor of 11. Since the original dimensions of 12 by 18 by 15 DO NOT contain a factor of 11, answer choice A is correct.

Answer:A

Scott Woodbury-Stewart
Founder and CEO
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