4 MI/II/11 A machine is used to generate codes consisting of 4 characters. A character is either one of the 26 letters of the alphabet A - Z or one of the 10 digits 0 - 9. Each of the 36 characters are equally likely to be generated and each character can be generated more than once. Find the probability that a randomly generated code has (i) no digits, [1] (ii) the first two characters consisting of digits and the first digit is higher than the second digit, [2] [3] (iii) three different letters and one digit, (iv) exactly two letters and two digits, such that the letters are the same or the digits are the same, but not both. [3]