Different international conventions that have been developed to represent odds.
Where a coin-toss has 50% probability for heads there are three common ways to represent the odds of the event:
Europe (Decimal) – 2.0
UK (Fractions) – Evens (or 1/1, or even money)
US (American) – +100; a (+) indicates the amount that would be won for every 100 bet placed. (-) indicates how much must be bet to win 100