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Probability of all of them choosing different numbers = n!/\(n^n\)
Probability of all of them choosing the same number = 1/ \(n^n\)

n!/\(n^n\) = 6* 1/ \(n^n\)
n! = 6
n = 3

Option A
Bunuel
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


 


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There are 1 to n integrers.
Probability that all choose different numbers = 1*(n-1)/n * (n-2)/n * ...... 1/n = (n-1)!/n^(n-1) --- A
Probability that all choose same number: 1/n^n --- B

It is given that
A = 6B
Upon substituting and simplifying we get:

(n-1)!=6/n

From the options, n=3 satisfies this relation.
Answer is A.

Bunuel
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


 


This question was provided by GMAT Club
for the GMAT Club Olympics Competition

Win over $30,000 in prizes such as Courses, Tests, Private Tutoring, and more

 

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Bunuel
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


 


This question was provided by GMAT Club
for the GMAT Club Olympics Competition

Win over $30,000 in prizes such as Courses, Tests, Private Tutoring, and more

 

Total outcomes = n^n
P(different) = n!
P(same) =n
=>
n!/n^n = 6n/n^n
n!= 6n
(n-1)!=6

Now, use trial and error for each of the option to make the equation correct.
Here we see for n=4
(4-1)!= 3!=6


ANSWER: B
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Each of the n people can choose a number from 1 to n, so each person has n option
So total options are n^n.

To choose same number

There are n possible outcomes one for each number from 1 to n.

Hence Probability each choosing same number is: n/n^n

To Each choose different number:
first person and has n option and second person has (n-1), 3rd has (n-2) options and so on
So total options are n!

Hence Probability each choosing different number is: n!/n^n

According to given condition

6*n/n^n = n!/n^n = 6*n = n!
6 = (n-1)!
3! = (n-1)!
n = 4

Option B.
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