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# gmat prep-4

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Senior Manager
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22 Aug 2009, 09:54
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67% (02:07) correct 33% (00:00) wrong based on 5 sessions

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I've got troubles to answer some of the gmat prep questions. The solutions will be appreciated with kudos . Thanks for the help
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Please give kudos if you enjoy the explanations that I have given. Thanks

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22 Aug 2009, 10:21
1
KUDOS
i went for the middle of the line and tried 3/7-2/5 to get 1/35. Now looking at the results you should see 1/70 could contend for answer but it is very suspicious since there's the LCM is 35 and they have it as 1/70.
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22 Aug 2009, 10:45
Please note my answers are wrong. So A is wrong in this case.
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22 Aug 2009, 11:25
1
KUDOS
Expert's post
Hey, I'll do anything for kudos

I am sure there is a fancy/elegant way to solve this question, but on the GMAT, I prefer dirty and reliable that will not result into any confusion and can be done one step at a time.

I would write out all of the possibilities like this:

5 segments: 0.2, 0.4, 0.6, 0.8 or fractions: $$\frac{1}{5}, \frac{2}{5}, \frac{3}{5}, \frac{4}{5}.$$
7 segments: 0.143, 0.286, 0.429, 0.572, 0.715, 0.858 (to find out 0.143 - I am dividing 100 by 7 to the third digit and the multiplying this number by 2, 3, 4, 5, and 6).
You can also do fractions: $$\frac{1}{7}, \frac{2}{7}....$$. What I notice immediately is that I will have to convert fractions to common denominators and that's an additional step/pain, so I'd rather stick with decimals.

Decimals are slightly off as it is technically 0.142857, but that should not be material (fingers crossed).

So, looking at the expressions, the least possible difference is between 0.572 and 0.6; (0.4 and 0.429 comes close as well but since the answer choice spread is so large, it does not matter which one you pick).
The difference is 0.0280 (approx) - don't confuse this with 0.280. this is somewhat smaller than $$\frac{1}{30}$$, and the number matching that in the answer choices is $$\frac{1}{35}$$.

Did I get it?

Edit: this is a longer solution than offered by shaselai - you have to figure out for yourself, which approach is least risky for you (least chance of making an error). Without writing it all out, it would probably take me a bit under a minute to solve it on the GMAT. Then, I would give it another read and cursory check to make sure I did not mess up in my calculations anywhere.
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22 Aug 2009, 11:59
3
KUDOS
Since you know you have to compare fractions. Write them at the very beginning with common denominator:

Large ticks: 1/5=7/35, 2/5=14/35, 3/5=21/35, 4/5=28/35
Small ticks: 1/7=5/35, 2/7=10/35, 3/7=15/35, 4/7=20/35, 5/7=25/35, 6/7=30/35

By looking at the fractions you can tell that the smallest distance 1/35 is between the second large tick 14/35 and the third small tick 15/35. It is also the distance between the third large tick and the fourth small.
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22 Aug 2009, 12:08
LenaA wrote:
Since you know you have to compare fractions. Write them at the very beginning with common denominator:

Large ticks: 1/5=7/35, 2/5=14/35, 3/5=21/35, 4/5=28/35
Small ticks: 1/7=5/35, 2/7=10/35, 3/7=15/35, 4/7=20/35, 5/7=25/35, 6/7=30/35

By looking at the fractions you can tell that the smallest distance 1/35 is between the second large tick 14/35 and the third small tick 15/35. It is also the distance between the third large tick and the fourth small.

I like this one!
Not sure if I would have been "smart" enough on the test to do it, but I like it!
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24 Aug 2009, 04:05
LenaA wrote:
Since you know you have to compare fractions. Write them at the very beginning with common denominator:

Large ticks: 1/5=7/35, 2/5=14/35, 3/5=21/35, 4/5=28/35
Small ticks: 1/7=5/35, 2/7=10/35, 3/7=15/35, 4/7=20/35, 5/7=25/35, 6/7=30/35

By looking at the fractions you can tell that the smallest distance 1/35 is between the second large tick 14/35 and the third small tick 15/35. It is also the distance between the third large tick and the fourth small.

Ditto. Thats how I did it.
+1 for you!
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24 Aug 2009, 07:39
3/7-2/5 = 1/35..OA B
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Re: gmat prep-4   [#permalink] 24 Aug 2009, 07:39
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