Show me your lunchbox!

There we go, numbers make more sense. I see what you guys mean now. The only thing I don't understand is why you are multiplying by 0.3 (I know it's representing the chance of passing)

70% chance of failure ^ 20 scrolls = 0.0008 (Rounded to 4 decimal places)
That would be constant for both cases.
Then 0.0008 ^ 70% (aka 0.7) chance of failure = 0.0068 (Again, rounded)
Or 0.0008 ^ 30% (aka 0.3) chance of success = 0.1176 (Rounded to 4 decimal places)

Either my calculator is pineappleed up or I got opposite results.

it's not 0.0008 ^ 70%/30%, it's 0.0008*0.7/0.3

You'll get a 0,00056 chance of missing another one, and 0,00024 chance of hitting.