antonag07 How did you calculate that?
Honestly, I just don't feel like looking it up in the description.
If you've already found a formula, could you write it down? How do the spell blocking percentages depend on the number of goblins and the level of the Sorceress?
Using the formula (Sorceress level + spell level + 17) x 25, it turns out that to block the "Charm" spell cast by a level 15 hero, you need 925 goblins. If there are 500 of them, then the probability of blocking should be (500/925)*100% = 54%.
Why did you get 15%?
Regarding the second statement (why not 54%, but 15% with 500 goblins) – see the manual for a detailed explanation of this issue...