Есть синие, красные и белые шары. Их всего 20. Из них 15-не синие, 12-не белые. Сколько к??асных шаров?

I was asked why I like reading books and I answered that books have been my best friends for many years. I answered that I was the only child in my family and that my parents are always busy at work, thats why  I used to spend a lot of time playing with my toys. Especially on holidays I was presented with wonderful new books: fairy tales, fantasy books, science fiction. As I have understood some of them were written ages ago. I enjoyed them very much. Thats why I believe books are the most ancient media

20-15=5 синие 20-12=8 белые 20-5-8=7красный