# You need to select a 5-character password for an account. You may use the digits 0-9 or the lower case letters a-z. You may repeat digits or letters. How many possible passwords are there?

${36}^{5}$
You can repeat characters, so every place is independent on the content of the others. This means that you have $36$ choices for the character in the first place, $36$ for the second, and so on. This means $36 \cdot 36 \cdot 36 \cdot 36 \cdot 36$ in total, which is ${36}^{5}$.