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The distribution of I.Q. scores can be modeled by a
normal distribution with mean
and standard deviation . An interactive
graph of this distribution is given below. To
use it, click and drag the red dot. (Be patient
-- the interactive applet may take a minute to load.)

What is the formula for the density function of I.Q.
scores?

Use the interactive graph to estimate the fraction
of the population with I.Q. between 75 and 120.