Official Solution:Artificial intelligence computer HAL 9000 randomly picks three distinct integers between 1 and 9000, inclusive. If the first number picked is \(a\), the second number picked is \(b\), and the third number picked is \(c\), what is the probability that \(a > b > c\) ? A. \(\frac{1}{60}\)
B. \(\frac{1}{30}\)
C. \(\frac{1}{20}\)
D. \(\frac{1}{6}\)
E. \(\frac{1}{3}\)
The question basically asks about the probability that three numbers picked are in decreasing order (\(a > b > c\)).
Any three numbers can be picked in \(3! = 6\) ways, and only one sequence from these 6 will be in decreasing order. So, the probability is \(\frac{1}{6}\).
For example, 2, 5, and 6 can be drawn in 6 ways ({firs number, second number, third number}): {2, 5, 6}, {2, 6, 5}, {5, 2, 6}, {5, 6, 2}, {6, 2, 5} and {6, 5, 2}. Only one from these 6 is in decreasing order: {6, 5, 2}.
Answer: D