Two cases:
1) if there are two numbers, that means a falloff between full and zero on that range, so in that case it's a falloff between 100% damage and 0% on the 2-5 range.
2) if there are three numbers (like 2/4/10), then the falloff is 0-2 from 50% to 100%, then constant 100% between 2-4, and falloff from 100% to 0% in the 4-10 range. This form is usually used with automatic weapons.