а) 7*2/30-3*3/30=5/30=1/6
б) 5/42:6/7=5/42*7/6=5*7/42*6=5/36
в) 4/10+2/3=12/30 + 20/30=1 2/30 = 1 1/15
36:9/7 -19.8 +17/6 =36*7/9 -19 .8 +17/6=28-19.8 +17/6=8 2/10 +17/6 =41/5+17/6=
246/30 + 85/30 = 331/30 = 11 1/30
2) 1.2х-0.8х=0,6-27 , 0,4х= -26.4 , х= -66