FERTIG!

m = 11 (slider from 2 to 53, step 1)
r = 7 (slider from 2 to 51, step 1)
r_{inv} = 8 (slider from 2 to 51, step 1)
Text1: "r \cdot r_{inv} = " + r + " \cdot " + r_{inv} + " \equiv" + (Mod[r * r_{inv}, m])
Text3: "(mod " + m + " )"