How to understand this case with non-mutually exclusive events in probability theory?

Question

Mathematics

Greetings!
Just started studying probability theory from scratch. Therefore, do not throw complex formulas: D
There is a seemingly simple Venn diagram:


The question is P (AUB) = ?
Answer 15% + 55% + 10% = 80%

It seems that there is an intersection and at the same time they are not mutually exclusive, including the intersection in the result led me to some confusion. I seem to understand what is happening here, because we are dealing with interest, but at the same time, not completely. I would like to hear other visions, how do you think in this case?

Answer 1

It seems that everything is correct.
A ∪ B is the union, the cases when it falls into any of the colored areas.
Or, more simply, they are interested in everything except the white 20%.
Both arguments give the same 80%.

Answer 2

Wikipedia