Răspuns:
1.a 3/4, 3/5, 3/3, 4/3, 4/4, 4/5, 5/3, 5/4 ,5/5.
1.b 8/4, 8/7, 7/4
1.c 3/13 + 5/13 = 8/13
1.d 21/6 - 9/6 = 2
(sper că te-am ajutat:)