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The logarithmic function y = logx + 7.9 can be used to determine the magnitude, y, of an earthquake given an intensity comparison, x, of a previous earthquake—in this case, an earthquake with a rating of 7.9 on the Richter Scale. This function is graphed below.

What is the magnitude of an earthquake, y, that is seven times as intense as the previous earthquake (rounded to the nearest tenth)? What intensity, x, is the aftershock with a magnitude of y = 8.9 (rounded to the nearest whole number) compared with the original 7.9 earthquake?

 A.)Magnitude of earthquake: y = 9.0, intensity comparison: x = 9 times

b.) Magnitude of earthquake: y = 8.7, intensity comparison: x = 4 times 

C.)Magnitude of earthquake: y = 39.0, intensity comparison: x = 2 times 

D.)Magnitude of earthquake: y = 8.7, intensity comparison: x = 10 times

 Feb 17, 2016
 #1
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7 times intense

 

y = log(7) + 7.9 = about 8.7

 

Intensity comparison

 

8.9 = log x  + 7.9      subtract 7.9 from both sides

 

1  = log x        and x = 10

 

So  (D)  is correct

 

 

 

cool cool cool

 Feb 18, 2016

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