1. How many bit strings of length four do not have two consecutive 0 s? 2. How many bit strings of length five do not have two consecutive 1s ? 3. How many bit strings of length five do not have two consecutive 0s? 4. How many bit strings are there of length six or less? HINT: use the sum rule, adding the number of bit strings of each length to 6 including the empty string 5. How many strings of four decimal digits (0,1,2,3,4,5,6,7,8,9) do not contain the same digit twice