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Arithmetic: How many times?? Please explain

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by Divya Ann Chacko » Tue Dec 10, 2013 5:13 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

Answer is option C
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Source: — Problem Solving |

by Brent@GMATPrepNow » Tue Dec 10, 2013 6:03 pm
Divya Ann Chacko wrote: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
If we start with a nice number, it won't take us long to list the intensity for each reading, starting at a reading of 3 and stopping at a reading of 8.

Say a reading of 3 means an intensity of 1
So, a reading of 4 means an intensity of 10
A reading of 5 means an intensity of 100
A reading of 6 means an intensity of 1,000
A reading of 7 means an intensity of 10,000
A reading of 8 has an intensity of 100,000

100,000 is 100,000 times bigger than 1.
Since 100,000 = 10^5, the correct answer is C

Cheers,
Brent
Brent Hanneson - Creator of GMATPrepNow.com
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