The distribution of I.Q. scores can be modeled by a normal distribution with mean $\mu = 100$ and standard deviation $\sigma = 15$. 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.)

1. What is the formula for the density function of I.Q. scores?
   $p(t) =$
   
   
2. Use the interactive graph to estimate the fraction of the population with I.Q. between 75 and 120.