Doua numere impartite care dau si rest proba lor se face:
D : I = C si restul r, proba D = C X I + r. 9 = 0+9, 1+8, 2+7, 3+6, 4+5,+5+4, 6+3, 7+2, 8+1 9+0 ⇒ ca: 9:5=1r4(F), 18:5=3r3(A), ..........63:5=12r3(A).............90:5=18r0(F)
A = adevarat, F =fals