These rules use the following die notations:
Die rolls are expressed in the format:
[#] die type [+/- modifiers]
Example: 3d6+2 means: "Roll 3 six sided dice. Add the result of the three dice together. Add 2."
In general, if you wind up with a fraction, round down, even if the fraction is one-half or larger.
Exception: Certain rolls, such as damage and hit points, have a minimum of 1.
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).
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 is 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.