Assumptions used to construct the model:
-- The coin has two sides.
-- The probability that the coin will land standing on its edge is zero.
-- The probability that the coin will land with one side up or
the other side up is 100% .
-- The coin is "honest". The probability of landing on one side
is equal to the probability of landing on the other side.
Conclusions / Probability model resulting from the assumptions:
The probability of either side up is 1/2 = 0.5 = 50% .