:4. Solution.  The first statement is true since the population
histogram follows the normal curve. <p>

The second statement is false since the SE of the
population incomes is $5,000, not $500. <p>

: the chance that X is between
$19,000 and $21,000 is either 0% or 100%. <p>

The fourth statement is true since the SE of the sample
average is $5.000/10 = $500. <p>

The correct answer is "two". <p>