Alexander the Great has the Hellenic League bonus in Civilization V, which means that "City-State influence degrades half as slowly as normal, and it recovers at twice the speed as for other civilizations". If I choose the Patronage social policy tree, which has the initial bonus "Adopting Patronage will cause Influence with City-States to degrade 25% slower than normal", does this mean that the influence will degrade 75% slower than normal? In other words, are the two effects cumulative?
Percent bonuses are additive
If you have racial 50% bonus and 25% social bonus, you should get in the end, as expected a 75% bonus.