All five dice are different.
There are six ways out of six for the first die to be different.
There are five ways out of six for the second die to be different.
There are four ways out of six for the third die to be different.
That would be
The opposite of none is at least one.
One cube is called a die.
The plural is dice.
You have five dice. What is the probability that you will get a pair on one roll?
If you mean exactly One Pair, the solution is more elaborate.
We have 6 choices for the value of the Pair.
The other three dice must have values which are
. . different from the Pair and from each other.