Is the number of seconds required to travel d1 feet at r1

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Is the number of seconds required to travel d1 feet at r1 [#permalink]

06 Dec 2012, 07:46

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52% (02:13) correct

47% (01:00) wrong

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[Reveal] Spoiler: OA

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Re: Is the number of seconds required to travel d1 feet at r1 [#permalink]

06 Dec 2012, 07:50

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Is the number of seconds required to travel d1 feet at r1 feet per second greater than the number of seconds required to travel d2 feet at r2 feet per second?

We need to find whether \frac{d_1}{r_1}>\frac{d_2}{r_2}.

(1) d1 is 30 greater than d2 --> d_1=d_2+30. Nothing about the rates. Not sufficient.
(2) r1 is 30 greater than r2 --> r_1=r_2+30. Nothing about the distances. Not sufficient.

(1)+(2) The question becomes whether \frac{d_2+30}{r_2+30}>\frac{d_2}{r_2}. Now, if d_2=r_2, then \frac{d_2+30}{r_2+30}=\frac{d_2}{r_2}, thus in this case the answer would be NO but if d_2=1 and r_2=2, then in this case \frac{d_2+30}{r_2+30}=\frac{31}{32}>\frac{1}{2}=\frac{d_2}{r_2}, thus in this case the answer would be YES. Not sufficient.

Answer: E.
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Re: Is the number of seconds required to travel d1 feet at r1 [#permalink]

18 Dec 2012, 06:35

Walkabout wrote:

Hi,

St1 and st 2 alone are not sufficient so combining we get

IS

(d2+30)/(r2+30) > d2/r2

The asnwer to this Question will depend upon the ratio of d2/r2.

If d2/r2 is <1, then on adding the same + ve qty to Num & Den will increase the ratio value
if d2/r2 is > 1 ,then on adding the same qty will decrease the ratio

Hence ans E

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Distance and Speed - Question 90 from OG13 [#permalink]

31 Jan 2013, 10:20

Is the number of seconds required to travel d1 feet at r1 feet per second greater than the number of seconds required to travel d2 feet at r2 feet per second?
(1) d1 is 30 greater than d2.
(2) r1 is 30 greater than r2.

Now, when I solved this question, I was surprised to see that the solution was (E), i.e, none of the statements provide sufficient information.

I recall, however, that when you add the same number to both the numerator and denominator of a fraction, the resulting fraction is always closer to 1. Using that logic, statements (1) and (2) TOGETHER provide sufficient information. Am I approaching this wrong here?

EDIT:

[Reveal] Spoiler:

Okay, figured it out. The information regarding which number is bigger (the speed or the distance) is not provided. Which means that the new fraction (r2 and d2) could actually be approaching 1 from either 0 or from infinity. Clever.

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Re: Distance and Speed - Question 90 from OG13 [#permalink]

31 Jan 2013, 10:44

Hi Absar,

As with all DS: translating the given information is critical

So the real question is: D1/R1 > D2/R2?

(1) D1 = D2 + 30 You can substitute one of the variables. BUT R1 and R2 could be anything so you could answer yes by making R1 very tiny number and R2 a huge number or you could do the opposite and the answer would be no. Insufficient.

(2) R2 = R2 + 30 The same logic as a above for this statement

(1) + (2) If you put the statements together the question becomes: D2+30/R2+30 > D2/R2

You should test very big values and very small values to see what happens. If R2 is a very tiny value and D2 is a massive value then the left side will be smaller than the right side because R2 will be increased by a much greater factor than will D2.

D2 = 1000 --------> 1030/31 > 1000/1 NO
R2 = 1

And vice-versa, if DS is a tiny value and R2 is a massive value than the left side will be greater because D2 will have a greater percentage increase than R2.

D2 = 1 ---------> 31/1030 > 1/1000 YES
R2 = 1000

So, you are able to say Yes and No to the original question so there the answer is E

Let me know if you have any questions on this!

HG.
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Re: Distance and Speed - Question 90 from OG13 [#permalink]

31 Jan 2013, 14:25

AbsarShah wrote:

[Reveal] Spoiler:

Merging similar topics. Please refer to the solutions above and ask if anything remains unclear.
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Is the number of seconds required to travel d1 feet at r1 feet p [#permalink]

15 May 2013, 23:41

kapilnegi wrote:

questions is t1 > t2?
or (d1/r1) > (d2 / r2)?
=> (d2 + 30)/(r2 + 30) > (d2/r2)?
=> [[(d2+30)-(r2+30)]/(r2 + 30)] > (d2-r2)/r2 -- subtract 1 on both sides
=> [(d2-r2)/(r2+30)]>(d2-r2)/r2
=> 1/(r2+30) > 1/(r2)
=> (r2+30) < r2
=> 30 < 0 ?
This questions IMO is not answerable but justified in OG . Any thoughts? Am I wrong?

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Re: Is the number of seconds required to travel d1 feet at r1 [#permalink]

16 May 2013, 01:29

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kapilnegi wrote:

This problem depends on the following concept.

If a,b are two positive numbers. and k is any positive number

a. if a/b is greater than 1 then a+k/b+k is less than a/b
b. if a/b is less than 1 then a+k/b+k is greater than a/b

Now consider the Above question

we have d1/r1 and d2/r2.

but d1 = d2 + 30
r1 = r2 + 30

so we have d2+30/r2 + 30 and d2/r2

but we don't know whether d2 is greater than r2. So together these statements are not sufficient
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Re: Is the number of seconds required to travel d1 feet at r1 fe [#permalink]

16 May 2013, 04:49

kiranck007 wrote:

kapilnegi wrote:

Merging similar topics.

The correct answer is E. Check here: is-the-number-of-seconds-required-to-travel-d1-feet-at-r1-143694.html#p1151497

Hope it helps.
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Re: Is the number of seconds required to travel d1 feet at r1 fe [#permalink] 16 May 2013, 04:49

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