①15:x=7:28
②34:x=0.25:8
③x:15=30:18
④14:56=x:113
803-207= ÷5= 798+150= + =
0.25×8= 1.5- = 7.5÷ = 0.77+0.3=
9.8-8= × = 45.54÷45= 24× =