In the picture below

(1) Subtracting the 7% from both is incorrect. This is easy to see by drawing a large circle to represents all bio majors, a mid-size circle (inside the big-circle) that takes up 52% of the area of the big circle to represent those bio majors who take stat, and a small-circle (inside the big-circle) that overlaps the mid-size circle to represent those bio majors who take computer science. The area of overlap of the mid-size circle and the small-circle is 7% of the total area of the large circle.

Now add the none overlap areas of the mid-size and small circle, and to that add the overlap:

You get (in percent) 52 + 23 - 7 = 68 %. That's .68.

(2) Consider only the students who have taken statistics. That's the mid-size circle in (1). And for these students what fraction have taken computer science? The fraction is 7/52 (and not 7% since we have limited the question to a specific group of students).

09-04-2011 at 10:50 pm

Step-by-step explanation: