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railway journey

by hemant_rajput » Sat Jan 26, 2013 10:41 am
Q2 . The duration of a railway journey varies as the distance and inversely as the velocity, the velocity varies directly as the square root of the quantity of coal used per kilometer , and inversely as the number of carriages in the train. In a journey of 50 km in half an hour with 18 carriages, 100 kg of coal is required . How much coal will be consumed in a journey of 42km in 28 min with 16 carriages.

a. 53.76
b. 179.33
c. 47.51
d. 48.43
e. None of these
[spoiler]oa:a[/spoiler]
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by Tommy Wallach » Sat Jan 26, 2013 4:38 pm
Hey Hemant,


First step. Before posting a question, please make sure there are no typos or errors. Even a couple missing words can make a question mega-confusing for folks, and I see a couple errors here. Also, this is not remotely a realistic question. There are no questions on the GMAT that require you to do problem solving math and then have an answer choice "none of the above". It does not happen. On may levels, this is NOT a realistic GMAT question. ALSO, the given information has a BUNCH of unnecessary information, which doesn't happen on the GMAT. In short, this is a ridiculous question. Now, onwards!

We know that a 50km journey that lasts 30 minutes and has 18 carriages, 100kg of coal is consumed.

The original velocity was 50/30 km per minute, or 5/3 . The new velocity is 42/28, or 3/2.

That relationship, (5/3)/(3/2), or 10/9, represents the square root of the quantity of coal per kg relationship, so that relationship should be 100/81.

We already know that the first journey required 2kg of coal per km, so:

2/x = 100/81 162 = 100x x = 1.6

42 * 1.6 = 67.2

So I guess the answer is None of the Above. Which would never happen on the GMAT. Ever. : )

-t
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by hemant_rajput » Sat Jan 26, 2013 9:38 pm
Tommy Wallach wrote:Hey Hemant,


First step. Before posting a question, please make sure there are no typos or errors. Even a couple missing words can make a question mega-confusing for folks, and I see a couple errors here. Also, this is not remotely a realistic question. There are no questions on the GMAT that require you to do problem solving math and then have an answer choice "none of the above". It does not happen. On may levels, this is NOT a realistic GMAT question. ALSO, the given information has a BUNCH of unnecessary information, which doesn't happen on the GMAT. In short, this is a ridiculous question. Now, onwards!

We know that a 50km journey that lasts 30 minutes and has 18 carriages, 100kg of coal is consumed.

The original velocity was 50/30 km per minute, or 5/3 . The new velocity is 42/28, or 3/2.

That relationship, (5/3)/(3/2), or 10/9, represents the square root of the quantity of coal per kg relationship, so that relationship should be 100/81.

We already know that the first journey required 2kg of coal per km, so:

2/x = 100/81 162 = 100x x = 1.6

42 * 1.6 = 67.2

So I guess the answer is None of the Above. Which would never happen on the GMAT. Ever. : )

-t

Hey Tommy,

Thanks for the solution. I'm sorry for the typo.
The reason why my question is having option, "none of these", because these questions are CAT Exam questions( similar to GMAT exam). I didn't know that the GMAT question don't have "None of these" as there option , but you can see that CAT do. My thought process was, if I can solve a question, it doesn't matter to which exam it belong. Although, now I clearly see that it matters. I'll keep that in mind before posting any question over here.
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by Tommy Wallach » Sat Jan 26, 2013 10:23 pm
Hey Hemant,

No problem at all, but yes, in the future, it's best not to post anything here that isn't at least intended to be a GMAT question. Even though the question you posted tests concepts that are on the GMAT (rates, ratios, etc.), the GMAT really doesn't focus so heavily on calculation. Also, the numbers are generally friendlier, and because there's no "none of the above" answer choice, you can often ballpark instead of actually solving.

Anyway, hope the explanation made sense. Oh, and if you're prepping for the GMAT right now, definitely only stick to GMAT materials.

Thanks!

-t
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by jkaustubh » Sat Jan 26, 2013 10:42 pm
hemant_rajput wrote:
Tommy Wallach wrote:Hey Hemant,


First step. Before posting a question, please make sure there are no typos or errors. Even a couple missing words can make a question mega-confusing for folks, and I see a couple errors here. Also, this is not remotely a realistic question. There are no questions on the GMAT that require you to do problem solving math and then have an answer choice "none of the above". It does not happen. On may levels, this is NOT a realistic GMAT question. ALSO, the given information has a BUNCH of unnecessary information, which doesn't happen on the GMAT. In short, this is a ridiculous question. Now, onwards!

We know that a 50km journey that lasts 30 minutes and has 18 carriages, 100kg of coal is consumed.

The original velocity was 50/30 km per minute, or 5/3 . The new velocity is 42/28, or 3/2.

That relationship, (5/3)/(3/2), or 10/9, represents the square root of the quantity of coal per kg relationship, so that relationship should be 100/81.

We already know that the first journey required 2kg of coal per km, so:

2/x = 100/81 162 = 100x x = 1.6

42 * 1.6 = 67.2

So I guess the answer is None of the Above. Which would never happen on the GMAT. Ever. : )

-t

Hey Tommy,

Thanks for the solution. I'm sorry for the typo.
The reason why my question is having option, "none of these", because these questions are CAT Exam questions( similar to GMAT exam). I didn't know that the GMAT question don't have "None of these" as there option , but you can see that CAT do. My thought process was, if I can solve a question, it doesn't matter to which exam it belong. Although, now I clearly see that it matters. I'll keep that in mind before posting any question over here.
In my opinion there is a lot of difference between CAT and GMAT. The level of quant questions in CAT is much higher than those asked in GMAT. Also as Tommy pointed out that there is no none of these options in GMAT. Hemant, these questions are more relevant in sites like Pagalguy.com
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by hemant_rajput » Sat Jan 26, 2013 10:49 pm
jkaustubh wrote:
hemant_rajput wrote:
Tommy Wallach wrote:Hey Hemant,


First step. Before posting a question, please make sure there are no typos or errors. Even a couple missing words can make a question mega-confusing for folks, and I see a couple errors here. Also, this is not remotely a realistic question. There are no questions on the GMAT that require you to do problem solving math and then have an answer choice "none of the above". It does not happen. On may levels, this is NOT a realistic GMAT question. ALSO, the given information has a BUNCH of unnecessary information, which doesn't happen on the GMAT. In short, this is a ridiculous question. Now, onwards!

We know that a 50km journey that lasts 30 minutes and has 18 carriages, 100kg of coal is consumed.

The original velocity was 50/30 km per minute, or 5/3 . The new velocity is 42/28, or 3/2.

That relationship, (5/3)/(3/2), or 10/9, represents the square root of the quantity of coal per kg relationship, so that relationship should be 100/81.

We already know that the first journey required 2kg of coal per km, so:

2/x = 100/81 162 = 100x x = 1.6

42 * 1.6 = 67.2

So I guess the answer is None of the Above. Which would never happen on the GMAT. Ever. : )

-t

Hey Tommy,

Thanks for the solution. I'm sorry for the typo.
The reason why my question is having option, "none of these", because these questions are CAT Exam questions( similar to GMAT exam). I didn't know that the GMAT question don't have "None of these" as there option , but you can see that CAT do. My thought process was, if I can solve a question, it doesn't matter to which exam it belong. Although, now I clearly see that it matters. I'll keep that in mind before posting any question over here.
In my opinion there is a lot of difference between CAT and GMAT. The level of quant questions in CAT is much higher than those asked in GMAT. Also as Tommy pointed out that there is no none of these options in GMAT. Hemant, these questions are more relevant in sites like Pagalguy.com
I agree with you, I'll keep in mind for future.
I'm no expert, just trying to work on my skills. If I've made any mistakes please bear with me.
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by Grindingitout » Mon Jan 28, 2013 3:06 am
The number of carriages also needs to be taken into consideration.

So the equation becomes (I am just adding on to what Tommy has updated above)

100/81 = (2/x) * (16/18) ^2

This will give the value of x = 1.28 (x being the Coal/km).

So final answer = 1.28 * 42 = 53.76

(only after i solved this that I realized its not a GMAT question ! :)
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