Does playing a low-level quest in Diablo III give me less XP per kill?

Question

If I've skipped to Act II as soon as I can, but I come back eventually and play with a level 3 player, the mobs are very easy.

Are they providing me with less XP per mob then I would've achieved if I were level 3? Are they providing my friend with less XP then if he were playing with another level 3 player?

Answer 1

Presumably, the reason they're easy is because you've outleveled them. Monsters below your level provide less experience, as seen in the table below.

Level difference is calculated as (mob level) - (character level).

Level difference  Multiplier 
+3 or more        125% 
+2                120% 
+1                115% 
 0                100% 
-1                 90% 
-2                 80% 
-3                 70% 
-4                 60% 
-5                 45% 
-6                 30%
-7                 15%
-8                  5%
-9                  1%
-10 or below        0%

Bonus XP/kill from gear is only applied if the monster is at most 5 levels below you.

Source: Click to Loot