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by karthikpandian19 » Thu Jul 05, 2012 11:35 pm
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) 8^3

(D) 3^8

(E) 7^8 - 4^8
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by GMATGuruNY » Fri Jul 06, 2012 2:04 am
karthikpandian19 wrote: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) 8^3

(D) 3^8

(E) 7^8 - 4^8
Whenever we move up one position in the scale -- from a reading of x to a reading of x+1 -- the intensity increases by a factor of 8.

Let the intensity of a reading of 4 = 1.
With each move up in the scale, the intensity increases by a factor of 8:
A reading of 5 = 8*1 = 8.
A reading of 6 = 8*8 = 8².
A reading of 7 = 8*8² = 8³.

The correct answer is C.
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by coolhabhi » Fri Jul 06, 2012 3:10 am
if x + 1 is 8 times x then

5 would be 8 times of 4 => 8*4

and

6 would be 8 times of 5 => 8*8*4

and

7 would be 8 times of 6 => 8*8*8*4

=> a reading of 7 is 8^3 more than a reading of 4
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by karthikpandian19 » Fri Jul 06, 2012 6:43 am
OA is C
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by karthikpandian19 » Fri Jul 06, 2012 6:44 am
OA is C
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