counting the empty string How many bit strings with length n

counting the empty string? How many bit strings with length not exceeding n, where n is a positive integer, consist entirely of Is, not counting the empty string?

Solution

we are given that nit string of length =n

and there should not be any empty string

so,

l=1,2,3,4....n

1+1+1+..+1=n

Answer is n