①x: 18=2 : 9
②x: 8=0.25 :
③
3+6+4=
8+5+2=
6+7-2=
19-3-5=
9+7-3=
14-4+6=
0.45×0.8 = 5.6÷10 =
2÷24= ×= 16×40%=
112= 51×99≈ 3.5×2÷3.5×5=