Suppose each laptop of a certain type is assigned a series number, which consists of a sequence of eight symbols: number, letter, letter, letter, number, number, number, number, where a letter is any one of 26 letters and a number is one among 0, 1, : : : , 9. Assume that all series numbers are equally likely. (a) What is the probability that all symbols are dierent if one laptop is picked at random with equal probability? (b) What is the probability that all symbols are dierent and the rst number is the largest among the numbers?