A 10 character sequence is generated by a random computer. Each character is selected independently and uniformly at random from the set of all letters (both capital and lower case) and numbers. That is {a,b,...,z}{A,B,...,Z}{0,1,...,9}.

• What is the probability that exactly 6 of the characters are digits?
• What is the expected number of digits in a sequence?
• What is the variance of the number of digits in a sequence?