Worked example
At decimal odds of 2.50, a hypothetical stake of 10 returns 25 if the bet wins, including the original 10. The net winning profit is 15; a losing selection can lose the full stake.
Inverse price and margin
One divided by the decimal price gives the implied probability before margin. In a complete two-outcome example, prices of 1.80 and 2.10 imply about 55.56% and 47.62%; the total is about 103.17%, not 100%.
What the calculation cannot tell you
Normalizing those inverse prices removes the excess total mathematically, but it does not establish true win probabilities. Different settlement rules, missing draw outcomes and different capture times can invalidate a comparison.