The total area under the curve must equal 1. Let the value of the density curve be x. Then 10x = 1. Therefore x = 1/10 or 0.1. The correct answer is D. 0.1.
The samples he chose may not be a representative sample because the number of students per foreign language class may not be the same. One class may have a very large number of students while another may have only a few. Taking equal number of students per class is not a representative sample.<span />
