Intensity scale readings

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BlueDragon2010: Senior | Next Rank: 100 Posts; Posts: 91; Joined: Tue Mar 31, 2009 11:19 amFollowed by: 1 member

by BlueDragon2010 » Sat Feb 08, 2014 9:09 am

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

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Source: Beat The GMAT — Problem Solving | Sat Feb 08, 2014 9:09 am

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Brent@GMATPrepNow: GMAT Instructor; Posts: 16207; Joined: Mon Dec 08, 2008 6:26 pmFollowed by: 1268 members; Location: Vancouver, BC; Thanked: 5254 times; GMAT Score:770

by Brent@GMATPrepNow » Sat Feb 08, 2014 9:11 am

BlueDragon2010 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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Patrick_GMATFix: GMAT Instructor; Posts: 1052; Joined: Fri May 21, 2010 1:30 amFollowed by: 98 members; Thanked: 335 times

by Patrick_GMATFix » Sat Feb 08, 2014 9:36 am

Each reading (n+1) is 10 times higher in intensity than the one below (n), so the next higher reading (n+2) will be 100 times (10^2) higher than the initial reading (n). Each time the reading is increased by 1, the intensity is multiplied by 10. So going from a reading of 3 to a reading of 8 will multiply the intensity by 10 5 times (multiply by 10^5). The full solution below is taken from the GMATFix App.

-Patrick

Check out my site: GMATFix.com

To prep my students I use this tool >> (screenshots, video)

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