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mygif
Jesus Said,
November 11th, 2010 @11:12 am  

You basically want to find the score at which the cumulative distribution function is 0.8. If F(z) is the CDF of the normal distribution, then you have

F^-1(0.8) = (x-500)/100
0.8416 = (x-500)/100
584.16 = x

So the closest score is 580.

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