a: 5 = c rest 4 c=1
a :5 = 1 rest 4
a = 5 x 1 + 4
a = 5 + 4
a = 9
a : 5 = c rest 4 c = 2
a : 5 = 2 rest 4
a = 2 x 5 + 4
a = 10 + 4
a = 14
b : 5 = c rest 3 c = 1
b : 5 = 1 rest 3
b = 1 x 5 + 3
b = 5 + 3
b = 8
b : 5 = c rest 3 c = 2
b : 5 = 2 rest 3
b = 2 x 5 + 3
b = 10 + 3
b = 13
(a + b) : 5 = c rest x
a =9 b=8
( 9 + 8 ) : 5 = 17 : 5 = 3 rest 2
a=14 b = 13
( a + b ) : 5 = c rest x
( 14 + 13) : 5 = 27 : 5 = 5 rest 2
observam ca prin impartirea lui a+b la 5 restul este totdeauna 2