Official Solution: Each of \(n\) people randomly selects an integer from 1 to \(n\), inclusive. If the probability that all of them choose different numbers is six times the probability that all of them choose the same number, what is the value of \(n\)? A. 3
B. 4
C. 5
D. 6
E. 8
Each person has \(n\) options, integers from 1 to \(n\), inclusive. So the total number of possible outcomes (denominator) is \(n^n\) in all cases.
1. All choose different numbers: The number of ways to assign \(n\) different numbers \((1, 2, ..., n)\) to \(n\) people is \(n!\)
So probability \(= \frac{n!}{n^n}\)
2. All choose the same number: This can happen in exactly \(n\) ways: all choose 1, all choose 2, ..., all choose \(n\)
So probability \(= \frac{n}{n^n}\)
We are given:
\(\frac{n!}{n^n} = 6 * (\frac{n}{n^n})\)
Cancel denominator:
\(n! = 6n\)
Substituting the answer choices, we see that only \(n = 4\) satisfies the equation: \(4! = 6 *4 = 24\).
Answer: B