Question

Your statistics teacher tells you that there is a 50% chance that a coin will land heads up. How would you state this chance in terms of a probability?

Answer 1

`0.5` or `1/2`

IF we have a fair coin there are two possibilities:
heads or tails

Both have an equal chance.

So you divide the favourable chances ("success") `S` by the total number of chances `T`:

`S/T=1/2=0.5=50%`

Another example:
What is the chance of rolling less than three with a normal die?
`S` ("success") = (1 or 2) = 2 possibilities
`T` (total) = 6 possibilities, all equally probable
Chance `S/T=2/6=1/3`

Extra:
Almost no real-life coin is completely fair.
Depending on the faces of the heads and tail, the centre of gravity may be a tiny bit on the heads or tail side.
This will only show on long term mega-flipping, but this has been done! Google!