Explain an error problem in each of the following:

a) 13/35=1/5, 27/73 = 2/3, 16/64 = 1/4
b) 4/5+2/3=6/8, 2/5+3/4=5/9, 7/8+1/3=8/11
c) 8 3/8-6 1/4=2 2/4, 5 3/8-2 2/3=3 1/5, 2 2/7-1 1/3=11/4
d) 2/3*3=6/9, 1/4*6=6/24, 4/5*2=8/10

This has been posted elsewhere, and is answered there.