(a) A bit string is a finite sequence of O's and l's. How many bit strings have length 7? bit strings (b) How many bit strings of length 7 begin with four O's? If a bit string of length 7 begins with four O's, then positions remain to be filled in. Since each of these positions can be filled with either a 0 or a 1, the number of bit string of length 7 that begin with four O's is (c) How many bit strings of length 7 begin and end with a 1? bit strings

Two n-digit integers (leading zeros allowed) are considered equivalent if one is a rearrangement of the other (for example 12033, 20331 and 01332 are considered equivalent five digit integers.)  a) We need to find the number of five digit integers that are not equivalent. b)We need to find the number of non equivalent five digit integers if the digits 1, 3 and 7 can appear at most once. c) When all three digits  (1,3,7) appear once.