In this instance, we are betting that tails will come up so the probability of this happening can be expressed as 1 out of 2, 1 to 2, 1:2 or 1 / 2. There are only two possible outcomes of a coin flip – either heads or tails will come up. Ask yourselves what is the probability of tails coming up the next time you flip the coin. The concept of probability can best be explained by giving the coin-flip as an example.

So in this instance, 1 represents the number of ways to win with a straight up bet, while 37 stands for the total number of possible outcomes. For every straight up bet, there are two possible outcomes – the player either wins or loses.

In European roulette, all 37 numbers have equal chances of coming up. The second number or 37 in our example, represents the overall number of possible outcomes. When the probability is expressed as a fraction, the first number stands for the expected frequency of a given event occurring. When the concept of probability is applied to roulette, it is expressed as “1 out of 37”, for example, or is written down as 1/37, which is the same thing. In casino games like roulette, however, the term denotes the likelihood that a given number will come up. Generally speaking, the term “probability” can be defined as the likelihood that a specific event or outcome will occur.