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A sensor measures the intensity

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by pnk » Mon Jul 05, 2010 4:49 am
A sensor measures the intensity of light on a scale where a reading of x+1 is 8 times as intense as a reading of x. On this scale, how much more intense is a reading of 7 than a reading of 4?

A) 3
B) 24
C) 8 'to the power' 3
D) 3 'to the power' 8
E) 7 'to the power' 8 - 4 'to the power' 8

OA - C
Last edited by pnk on Mon Jul 05, 2010 6:51 am, edited 1 time in total.
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by Patrick_GMATFix » Mon Jul 05, 2010 5:27 am
You left out a key number between "is" and "times" in your stem. We need to know the multiplier :-)
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by pnk » Mon Jul 05, 2010 6:53 am
Patrick_GMATFix wrote:You left out a key number between "is" and "times" in your stem. We need to know the multiplier :-)
Corrected; Thanks Patrick
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by kvcpk » Mon Jul 05, 2010 7:15 am
Let the intensity of reading of 4 be I
then intensity of reading of 5 is 8 *I
then intensity of reading of 6 is 8^2*I
then intensity of reading of 7 is 8^3*I

hence C
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by jeremy8 » Mon Jul 05, 2010 7:16 am
If a reading of x+1 is 8* as intense as a reading of x, then a reading of 7 is 8*8*8 times more intense than a reading of 4, since 7=4+3.

A reading of 5 would be 8* more intense than a reading of 4.

A reading of 6 would be 8* more intense than a reading of 5 and therefore 8*8 times more intense than a reading of 4, or 8^2.

A reading of 7 would be 8* more intense than a reading of 6, therefore 8*8*8, or 8^3 times more intense than a reading of 4, so the right answer is C.

I think....
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