1/2*2/3*3/4-2/3*3/4*4/5-3/4*4/5*5/6=(1*2*3/2*3*4)-(2*3*4/3*4*5)-(3*4*5/4*5*6)=6/24-24/60-60/120=1/4-2/5-1/2=(5-8-10)/20=-13/20
1/2*2/3*3/4-2/3*3/4*4/5-3/4*4/5*5/6=(1*2*3/2*3*4)-(2*3*4/3*4*5)-(3*4*5/4*5*6)=6/24-24/60-60/120=1/4-2/5-1/2=(5-8-10)/20=-13/20