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# A scientist invented a Lamp that can give light

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Manager
Joined: 11 Aug 2012
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A scientist invented a Lamp that can give light [#permalink]  14 Nov 2012, 09:58
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A scientist invented a Lamp that can give light for about 130 hours, rounded to the nearest 10 hours, and used 10 gallons of oil, rounded to the nearest gallon. The actual number of hours per gallon that the lamp lighted must have been between

A. $$\frac{125}{10.5}$$ and $$\frac{135}{9.5}$$

B. $$\frac{135}{10}$$ and $$\frac{125}{9.5}$$

C. $$\frac{125}{9.5}$$ and $$\frac{135}{10.5}$$

D. $$\frac{130}{10.5}$$ and $$\frac{130}{9.5}$$

E. $$\frac{135}{10.5}$$ and $$\frac{125}{9.5}$$

I don't understand why the correct answer should be: $$\frac{125}{10.4}$$ and $$\frac{134}{9.5}$$.

If the actual number of hours is 10.5, it should be rounded to 11. And if the actual number of galons is 135, it should be rounded to 140.

Source: grockit.com
[Reveal] Spoiler: OA
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Joined: 30 Dec 2010
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Re: A scientist invented a Lamp that can give light [#permalink]  14 Nov 2012, 10:37
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Please read the answer. It says between 125/10.5 and 135/9.5. I had a second thought why the answer is not 125/9.5 and 135/10.5. But on close observation, I realized that with 125/10.5 and 135/9.5, the left and right boundary or the range value actually increases and so it satisfies the condition. The answer should be A) between 125/10.5 and 135/9.5.
Manager
Joined: 05 Nov 2012
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Re: A scientist invented a Lamp that can give light [#permalink]  14 Nov 2012, 13:47
danzig wrote:
A scientist invented a Lamp that can give light for about 130 hours, rounded to the nearest 10 hours, and used 10 gallons of oil, rounded to the nearest gallon. The actual number of hours per gallon that the lamp lighted must have been between

A. $$\frac{125}{10.5}$$ and $$\frac{135}{9.5}$$

B. $$\frac{135}{10}$$ and $$\frac{125}{9.5}$$

C. $$\frac{125}{9.5}$$ and $$\frac{135}{10.5}$$

D. $$\frac{130}{10.5}$$ and $$\frac{130}{9.5}$$

E. $$\frac{135}{10.5}$$ and $$\frac{125}{9.5}$$

I don't understand why the correct answer should be: $$\frac{125}{10.4}$$ and $$\frac{134}{9.5}$$.

If the actual number of hours is 10.5, it should be rounded to 11. And if the actual number of galons is 135, it should be rounded to 140.

Source: grockit.com
I expect you to be asking why answer shouldn't be $$\frac{125}{10.4}$$ and $$\frac{134}{9.6}$$
You did analyse it correctly but what if gallons consumed is 9.51? Mathematics say that 9.59 is rounded to 9.6 which is again as per question rounded to 10 gallons.... you are missing set of solutions between 9.55-9.59 and 10.41-10.44..... you cannot loose any answer solutions....
also the question was "have been between" so your range doesn't include all solutions. Hope it is clear.
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Re: A scientist invented a Lamp that can give light [#permalink]  09 Nov 2014, 06:33
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Manager
Joined: 31 Jul 2014
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Re: A scientist invented a Lamp that can give light [#permalink]  10 Nov 2014, 21:55
danzig wrote:
A scientist invented a Lamp that can give light for about 130 hours, rounded to the nearest 10 hours, and used 10 gallons of oil, rounded to the nearest gallon. The actual number of hours per gallon that the lamp lighted must have been between

A. $$\frac{125}{10.5}$$ and $$\frac{135}{9.5}$$

B. $$\frac{135}{10}$$ and $$\frac{125}{9.5}$$

C. $$\frac{125}{9.5}$$ and $$\frac{135}{10.5}$$

D. $$\frac{130}{10.5}$$ and $$\frac{130}{9.5}$$

E. $$\frac{135}{10.5}$$ and $$\frac{125}{9.5}$$

I don't understand why the correct answer should be: $$\frac{125}{10.4}$$ and $$\frac{134}{9.5}$$.

If the actual number of hours is 10.5, it should be rounded to 11. And if the actual number of galons is 135, it should be rounded to 140.

Source: grockit.com

I don't understand this question at all, can someone please explain...
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Re: A scientist invented a Lamp that can give light [#permalink]  10 Nov 2014, 22:43
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Let's look at the original source of this question, the Official Guide to GMAT, from which it has been copied . Here is the full original question:

On a recent trip, Cindy drove her car 290 miles, rounded to the nearest 10 miles, and used 12 gallons of gasoline, rounded to the nearest gallon. The actual number of miles per gallon that Cindy's car got on this trip must have been between

A. 290/12.5 and 290/11.5
B. 295/12 and 285/11.5
C. 285/12 and 295/12
D. 285/12.5 and 295/11.5
E. 295/12.5 and 285/11.5

Discussion here: on-a-recent-trip-cindy-drove-her-car-290-miles-rounded-to-99378.html
Video explanation here: http://www.gmatquantum.com/official-gui ... -2015.html

Cheers,
Dabral
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Manager
Joined: 31 Jul 2014
Posts: 83
GMAT 1: 630 Q48 V29
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Kudos [?]: 19 [0], given: 345

Re: A scientist invented a Lamp that can give light [#permalink]  10 Nov 2014, 22:59
dabral wrote:
Let's look at the original source of this question, the Official Guide to GMAT, from which it has been copied . Here is the full original question:

On a recent trip, Cindy drove her car 290 miles, rounded to the nearest 10 miles, and used 12 gallons of gasoline, rounded to the nearest gallon. The actual number of miles per gallon that Cindy's car got on this trip must have been between

A. 290/12.5 and 290/11.5
B. 295/12 and 285/11.5
C. 285/12 and 295/12
D. 285/12.5 and 295/11.5
E. 295/12.5 and 285/11.5

Discussion here: on-a-recent-trip-cindy-drove-her-car-290-miles-rounded-to-99378.html
Video explanation here: http://www.gmatquantum.com/official-gui ... -2015.html

Cheers,
Dabral

Thank you Now it is clear to me
Re: A scientist invented a Lamp that can give light   [#permalink] 10 Nov 2014, 22:59
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# A scientist invented a Lamp that can give light

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