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7) (5/12+1/8):3/8=(10+3)/24*(8/3)=(13*8)/(24*3)=13/9
8) 5/12+1/8:3/8=5/12+(1*8)/(8*3)=5/12+1/3=5/12+4/12=9/12=3/4
9) ...=20/7:(5/6-9/14)=20/7:(35-37)/42=20\7:8/42=20/7:4/21=20*21/7*4=20*3/1*4=60/4=15
10)...=20/7:5/6-9/14=(20*6)/(7*5)-9/14=(4*6)/7-9/14=24/7-9/14=48/14-9/14=39/14
11)...=9/4:15\11-3/8:7/8=(9*11)/(4*15)-(3*8)/(8*7)=33/20-3/7 =(231-60)/140=171/140=
= $1 \frac{31}{140}$
12)....=(19/6-36/6:62\15)*3/92= $(- \frac{17}{6} : \frac{62}{15} )* \frac{3}{92} =- \frac{17*15}{6*62} * \frac{3}{92} =- \frac{17*5}{2*62} * \frac{3}{92}$ = $\frac{17*5*3}{2*62*92}=$