simple. first, sum all factors those AR+, (dex works here,
+2 AR per dex) and let this A

second, sum all factors those AR * %, (usually skill, some
uniques have this feature) and let this B

your final AR : A * (B+100)(%)

example;

Gothic Bow have AR+130, ring A AR+70, ring B AR+100,
overall dex 400. sum, A is 1100.

Penetrate lv8 105%, frendly paladin's fanaticism lv6 65%.
sum, B is 170

your final AR : 270% of 1100 = 2970

regards,