Răspuns :
3\4=5/4-2/4 , 2/5=6/5-4/5 , 3/8=5/8-2/8 , 9/9=1, 13/11=25/11-12/11
3/4=1/4+2/4
2/5=1/5+1/5
3/8=2/8+1/8
9/9=5/9+4/9
13/11=10/11+3/11
2/5=1/5+1/5
3/8=2/8+1/8
9/9=5/9+4/9
13/11=10/11+3/11