3/4-5/6=9/12-10/12=-1/12
-1/12*3=-1/4
3/4+5/6=9/12+10/12=19/12
19/12*4=19/3=6 1/3
-1/4+6 1/3=-3/12+6 4/12=6 1/12
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1/2+2/3=3/6+4/6=7/6
7/6:5/6=7/6*6/5=7/5=1 2/5
1/2-2/3=3/6-4/6=-1/6
12*(-1/6)=-2
1 2/5-(-2)=1 2/5+2=3 2/5