[3/4+1/5]*5/19=19/20*5/19=1/4
[12 1/3 - 7 3/4]*6/11=[12 4/12 - 7 9/12]*6/11=4 7/12*6/11=55/12*6/11=2.5
[2 3/5 - 5/8]/19 3/4=[2 24/40-25/40]/19 3/4=1 39/40 / 19 3/4 =79/40 / 79/4=0.1
9 2/7 * 1 2/5 / 13 + 6 3/7 = 35/7 * 7/5 /13 + 6 3/7=49/91+ 6 39/91=6 88/91