We usually write numbers in decimal form (or base 10), meaning
numbers are composed using 10 different “digits” {0,1,...,9}.
Sometimes though it is useful to write numbers in hexadecimal or
base 16. Now there are 16 distinct digits that can be used to form
numbers: {0,1,...,9,A,B,C,D,E,F}. So for example, a 3 digit
hexadecimal number might be 3B8. (a) How many 2-digit hexadecimals
are there in which the first digit is E or F? Explain your answer in
terms of the...