AAMC 7 Question 43

[kabtq9s]

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I'm sure this is a classic case of "making it harder than it is" but I just can't see how they did it.

how do we know that its supposed to be d2/d1 and not d1/d2? and do we plug it back into the (L/d)^3 equation? if so then what is the value of L ?


http://mysowar.files.wordpress.com/2012/06/amcas-7-43.jpg

Thanks in advance

 

[LoLCareerGoals]

This is a simple algebra question.
Distortion magnitude is (L/d)^3, then ratio of distortion produced at d1 to distortion produced at d2 is:

(L/d1)^3 d2^3 4L
------------- = ------------- = (--------------)^3 = 1/64
(L/d2)^3 d1^3 16L

The value of L cancels. So it doesn't matter.