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    A mixture of spherical interstellar dust grains has a size distribution n(a)da which is pro- portional to a−αda, with α = 3.5, where a is the radius of a grain and n(a) is the number of grains of that radius per unit volume. If the minimum and maximum grain radii are amin = 0.01 μm and amax = 0.25 μm, calculate the mean grain radiusName:  Untitled.jpg
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    (Original post by charlotteflanagan)
    This is more statistics than physics. If you have a continuous probability distribution function f(x) between a and b, then what is the formula for the mean of x?
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