1.[(3/7 + 4/21) : (1/12 + 1/14) - 1/3*1/5] × 10=(60/15-1/15)*10=[(60-1)/15]*10=
=59/15*10=(59*10)/15=(59*2)/3=118/3
2.
a) 3/10 × 28/9 × 1/2*2/14=(3*28*2)/(10*9*2*14)=(3*28)/(10*9*14)=(3*2)/(10*9)=2/(10*3)=1/(5*3)=1/15
b) 2/5 × (1/4*1/7 - 1/3*1/14)=(2/84)/5=2/(84*5)=1/(42*5)=1/210
c) 1/6*6/11 × (5/24 + 2/3 × 21/36)=[(15/72)+(28/72)]/11=43/(72*11)=43/792
d) (2 + 16/7) × 6/45 - 2/90 × 3/4)=30/7*7/60=(30*7)/(7*60)=30/60=1/2