tween 3.9 and 4.1 long. From a large batch of bolts,
            a sample of 50 show a mean length of 3.95 with standard deviation 0.1.
            Assuming a normal distribution, what proportion is usable? The true sample
            mean is unknown, but we can use the sample mean and standard deviation
            to find approximate solutions.
          </p>
<pre class="programlisting">    <span class="identifier">normal</span> <span class="identifier">bolts</span><span class="special">(</span><span clas