You roll a balanced 6sided die 9 times in a row and you obse

You roll a balanced 6-sided die 9 times in a row and you observe the sequence of numbers.

(a) How many outcomes contain only 1’s, 2’s and 3’s? Eg., the sequence of all 1’s should be counted.

(b) How many outcomes have exactly four 1’s, three 2’s, and two 3’s (and, therefore, no 4’s, no 5’s and no 6’s)?

Solution