Bernoulli or Geometric Distribution

Would you advise me please on what is appropriate distribution calculation here

and how to set it up:

An unbiased coin is tossed repeatedly until a “tail” is observed for the second time.

Find the probability that it would require k tosses to achieve that

**Disclamer:**

This is a practice problem for entrance exam, and not a homework. If confirmation is needed send e-mail and I will send link to a problem on the web.

Re: Bernoulli or Geometric Distribution

Since a Bernoulli Distribution is defined only for a single experiment (one toss, in this case), this rather rules out the Bernoulli.

Re: Bernoulli or Geometric Distribution