In a Venn diagram consisting of three intersecting circles where each circle represents students studying a different subject, the numbers inside the regions represent the count of students. If the region common to all three circles contains the number 3, how many students study all three subjects?

In a Venn diagram consisting of a rectangle, a circle, and a triangle, if the region enclosed by both the rectangle and the circle but not by the triangle is labeled with a specific number, and that number is 4, which option correctly identifies this value?

In a certain Venn diagram representing professional and demographic categories, if a triangle represents doctors, a rectangle represents women, and a circle represents postgraduates, which region representing the intersection of all three shapes gives the total number of postgraduate female doctors as 15?