how does work the total sum of physichal protection items?

Question

I tought that the protection given by the equipment was the sum of the physical protection of all them.

like 

Item	Physichal Protection
	5%
	5%
	2%
	2%
final protection	14%

But they told me that isn't how it works. 

How does really work it?

Answer 1

If you have 2 items with 5% and 2 items with 2% physical Protection, you can take

(1 - 0.05) * (1 - 0.05) * (1 - 0.02) * (1 - 0.02) = 0.95 * 0.95 * 0.98 * 0.98 = 0.866761 . So the sum of your physical protection is 1 - 0.866761 = 0.133239

That means, you will receive around 100 * 0.866761 = 86.6761 % of the damage.