Probability distribution pin code guessing

[Max.Planck]

Homework Statement

What is the distribution of stochastic variable X = "the number of attempts needed to find the correct last digit of a pin code"

Homework Equations

The Attempt at a Solution

I thought it was like this:
P(X=1) = 1/10
P(X=2) = 9/10*1/9
P(X=3) = 9/10*8/9*1/7
...
...
P(X=10) = 9/10*8/9*7/8*6/7*5/6*4/5*3/4*2/3*1/2*1

Thank you!

 

[Ray Vickson]

Homework Statement

What is the distribution of stochastic variable X = "the number of attempts needed to find the correct last digit of a pin code"

Homework Equations

The Attempt at a Solution

I thought it was like this:
P(X=1) = 1/10
P(X=2) = 9/10*1/9
P(X=3) = 9/10*8/9*1/7
...
...
P(X=10) = 9/10*8/9*7/8*6/7*5/6*4/5*3/4*2/3*1/2*1

Thank you!

Looks good.

RGV

 

[Max.Planck]

Looks good.

RGV

Thanks. Is it possible to capture P(X=x) in a formula?