-4.2x*(-6y) = 25.2xy
8m + 5p - 13m - p= -5m + 4p
k - (17 - k) + (-k + 30) = k - 17 + k - k + 30 = k + 13
-6*(4 + a) + 8*(a-6) = -24 - 6a + 8a - 48 = -72 + 2a
2,7:(-9/10)=2,7:(-0,9)=27:(-9)=-3
1/2 + 1/3 + 1/6 = 3/6 + 2/6 + 1/6 = 6/6 = 1
35+7*8+20=60
7*8=56
35+56+20=111,а не 60