Here is a chart for 'Root'. You can ignore the low and high partial lines, since they don't have any bearing on roots.
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And here is the results of 20,000 simulated casts against 120MR:
Spell Name:
Root Resist Mod: 25
Casts: 20000 Full Hits: 0 Partials 2305 Resists: 17695
Resists Percent: 88.47% Average Partial: 38.18
Average Damage: 0.00