Average number of repetitions at given chance of success

Hi everyone,

First of all, English is not my native language.
I have this problem that i don't know how to solve.

What is the average number of repetitions for success, if chance of success is 1/10?

Thanks alot

-Lasse

<Expected number of successes> = N * <Probability of a success>

Insert 1 on the left-hand side, and 1/10 on the right-hand side and solve for N.