<PRE><B>Question 336880</B>
Do it like this one:
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The intensity I of light from a light bulb varies inversely as the square of the distance d from the light bulb. Suppose I is 640 w/m^2 when the distance is 8m. How much farther would it be to a point where the intensity is 90 w/m^2?
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 k is a constant, d = distance
640 = k/8^2 = k/64
k = 40960
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For 90 w/m^2:
90 = 40960/d^2
d^2 = 40960/90
d = 64/3 meters 
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