Operations on rational numbers

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Operations on rational numbers

by C » Wed Apr 21, 2010 10:42 pm
On a scale that measures the intensity of a certain phenomenon, a reading of n + 1 corresponds to an intensity that is 10 times the intensity corresponding to a reading of n. On that scale, the intensity corresponding to a reading of 8 is how many times as great as the intensity corresponding to a reading of 3?

A) 5

B) 50

C) 10^5

D) 5^10

E) 8^10 - 3^10

OA is C

Source is OG 12th ed. PS 98.

Someone please explain the approach to this problem.

Thanks.
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by DeepthiRajan » Wed Apr 21, 2010 10:55 pm
According to the ques stem:

Reading Intensity

n x

n+1 10x

given

3 x
4 10x
5 (10)^2 x
6 (10)^3 x
7 (10)^4 x
8 (10)^5 x

Hence the intensity of 8 is (10)^5 times x---->(C)

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by tpr-becky » Thu Apr 22, 2010 10:10 am
This is a sequence problem in which each number is 10 times the number before it, therefore a reading of 4 will be 10 times a reading of three, and a reading of 5 will be 100 times a reading of three - 6 is 1000 times a three, 7 is 10000 times a three and 8 is 100000 a three.
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by frank1 » Sat Apr 24, 2010 8:31 am
at least in this question
if one has to make guess first,
1 and 2 cannot be answer as if seems too low (increasing 10 times means much higher)
4 and 5 is saying same thing (in GMAT they dont make your task easy like this ..lol)
so left is 3

but as already said,works only for this one...
but i think one learns technique here and digits are not important