HELP PLS! I'm studying for UCAT as I want to get into medicine. I don't understand probability diagrams like these, please explain it to me.

 80 (choice B)

Explanation:

This is an interesting venn diagram. Each region is either a circle or some kind of arrow shape. The numbers in the regions correspond to the qualities mentioned. For example, the "55" in the circle outside the other arrow regions tells the reader that there are 55 secretaries who are reliable but don't possess any other quality. As another example, the 35 is inside the circle and the left-pointing arrow to tell us that there are 35 people who are reliable and organized.

What we want to find are the values that are in 3 or more regions. There's only two cases when this happens: The 15 and the 65 as they are in the circle, the double arrow, and one of the single pointing arrows. So we have 15+65 = 80 candidates that possess 3 qualities. No person has all four qualities because there isn't a value that's in all four regions at the same time. Or you could note that the left and right pointing arrows do not overlap which is a big clue that there's no way someone could possess all four qualities at once. It might help to trace out the figures using different colors so you can pull apart the four figures.

phosphate, calcium ion, chloride ion, neon atom

step-by-step explanation: