ab5 divizibil cu 3=>
a+b+5=M3
a+b+5={6,9,12,15,18,21}=>
a+b={1,4,7,10,13,16}
1) a+b=1=>
ab5=105
2) a+b=4
=> ab5={135,225,315,405}
3) a+b=7=>ab5={165,255,345,435,525,615;705}
4) a+b=10=>ab5={195,285,375,465,555,645,735,825,915}
5) a+b=13=>ab5={495,585;675,765,855,945}
6) a+b=16=>ab5={795,885,975}
nu scrie
in cerinta ca a trebuie sa fie diferit de b, deci luam si cazurile cand a=b
in total
avem 30 de fractii care se simplifica cu 3
