|d20 Modern System Reference Document|
These rules use the following die notations:
Die rolls are expressed in the format:
In general, if you wind up with a fraction, round down, even if the fraction is one-half or larger.
Sometimes a special rule makes you multiply a number or a die roll. As long as you're applying a single multiplier, multiply the number normally. When two or more multipliers apply, however, combine them into a single multiple, with each extra multiple adding 1 less than its value to the first multiple. Thus, a double (x2) and a double (x2) applied to the same number results in a triple (x3, because 2 + 1 = 3).
BASIC TASK RESOLUTION SYSTEM
These rules assume a standardized system for determining the success or failure of any given task. That system is:
d20 + Modifiers vs. Target Number
The Modifiers and Target Number are determined by the type of task.
If the result of the d20 roll + the Modifiers equals or exceeds the Target Number, the test s successful. Any other result is a failure.A "natural 20" on the die roll is not an automatic success. A "natural 1" on the die roll is not an automatic failure, unless the rules state otherwise.