Problem: We have 40 books on a shelf randomly arranged. Three books are a series and have numbers - 1,2,3. Need to find the probability that they'll be arranged at ascending order, like 1 comes earlier than 2, and 2 earlier than 3, but they need not to be right after each other. Like this case is possible (1.....2......3)
Now I managed to find the probability when 123 come right after each other. It is about $0.00064$. But I can't find a strategy to solve the above mentioned one. Help would be very appreciated.