4/5 : 3/13 = 4/9 : 16/45= 6 10/13 : 1 5/39 = 55: 11/12 = 18/19:6=
4/5:3/13=4/5•13/3=52/15=3 7/15; 4/9:16/45=4/9•45/16=20/16=10/8=5/4=1 1/4; 6 10/13:1 5/39=88/13•39/44=2•3=6 18/19:6=18/19•1/6=3/19;