Hi

I would appreciate if someone could explain how to solve the following problem:

"How many different five letter "words" can you write with the letters BILBANA"

The answer is 690 but I'm not entirely sure how to get there. I divide the problem into different cases:

A+B = 5!

A+A = 5!/2!

B+B = 5!/2!

A+B+B = ?

A+A+B = ?

A+A+B+B = ?

Thanks in advance