Statistics and Probability

If all the six-digit numbers formed by using the digits from the set {1, 2, 3, 4, 5, 6}, without repetition, are listed from least to greatest, which number will be the 600th in the list? Hints: 1. How many numbers are there in the list? 2. What is the first number in the list? the last number in the list? 3. How many numbers are between the first number (whose leftmost digit is 1) and the least number whose leftmost digit is 2? In other words, how many six-digit numbers are formed from the set above (without repetition) where the left-most digit is fixed? Can you detect a pattern