This better not be your homework..

The chance of getting any number on any one roll is (1/18).

In this case, you are asking the chances of a specific number for 5 of the rolls.

(1/18) represents one side of the die for one roll. Multiply for each roll.

Thus, (1/18)^(5) is the chance of getting the same number for 5 rolls.

Correct me if I am wrong.

The same chance of you getting laid.

Lucky explained it right.

In probability there are two concepts (yes there are actually more, but for the purposes of this argument there are 2)

The two routes are OR and AND.

AND means you want two or more things to all happen together
OR means you want any of two or more things to happen

Self explanatory no?

So it's quite simple.

AND = multiply
OR = add

So if you want to know the chance of having one number AND the same number again on that die, you take the probability of the first (1/18) multiplied by the probability of the second condition (1/8).  In this case, you just extend it out 3 more times. 

It's funny because neither of you actually read the full exercise.
The probability for getting 5 out of five is not the same as getting 5 out of 6.