# 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?

Jan 14, 2015

$0.5$ or $\frac{1}{2}$

IF we have a fair coin there are two possibilities:

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 $\frac{S}{T} = \frac{2}{6} = \frac{1}{3}$

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!