A single monster increase in XP value by 25 from levels 1 through 4. So a level 1 monster is 100 xp, a level 2 is 125 xp.
Take this to the next logical conclusion, a party of 5 monsters goes from being worth 500 to 625 XP.
One step farther, 8-10 encounters of this type would require 4,000 to...