Warcraft/ Frozen Throne - Dota Item Effect Calculation

Inside Dota, We know that most item effect is not direct stack, example with 1 basher hero will gain 15% of stun chance, but with 2 basher is not equal to 2 X 15% = 30% of stun chances.

The actual formula of multiple item should calculate based on :
Total % = Current % / 100 + (100 - Current %)/100 * Additional %/100

Let make an example,
A hero with basher ability 25%, after equip one basher which got 15% bash effect,
according formula, total % to make a bash effect will be,

Total % = 0.25 + (100 - 25)/100 * 0.15
= 0.25 + 0.75 * 0.15
= 0.25 + 0.1125
= 0.3625

So hero will has 36.25% of bash effect instead of 25% + 15% = 40% bash effect.

So what if equip another basher again ? So % will calcualte base on.

Total % = 0.3625 + (100-36.25)/100 * 0.15
= 0.3625 + 0.0956
= 0.4581

Hero will end up with 45.81% of bash effect but not 25% + 15% + 15% = 55% of bash effect.