There's no such thing as a fair dice, perhaps a fair die.

Since there are 6 numbers on a die, and 1, 3, 5 represent 50% of the available number, the probability of getting one of those 3 numbers is 50% on every toss.

1/2

With one die, you have a 1:6 chance of rolling a 1.
You have a 1:6 chance of rolling a 3.
You have a 1:6 chance of rolling a 5.
There are six numbers on the die.  You are wondering about three of them.  3:6  = 1:2 = 50/50.

You'll find it in your Statistics Textbook.