Geometric Distribution Question

[James...]

Homework Statement

An experiment consistion of tossing three fair coins is performed repeatedly and "success" is when all three show a head.

What is the probability that the success is on the third performance of the experiment?

Homework Equations

Geometric distribution equation

p(x) = \theta(1-\theta)\stackrel{(x-1)}{}

where \theta is the probability of success

The Attempt at a Solution

The probability of getting heads on a fair coin is 1/2

so the probability of 3 heads is 1/8 which is \theta

I'm assuming the third trial is when x=3 so

p(3) = (1/8)*(1-(1/8))^2

p(3) = 0.095703125...Am I correct in my working/method for this question?

Many thanks

James

 

[CompuChip]

Looks fine to me!

 

[James...]

Cheers! I know the actualy calculation is done right. Just wasn't completely sure if I'd used the right method.

I stupidly left the notes I did for the question at University and I'm revising now at home so can't check over them.