分析:根據(jù)“積÷一個因數(shù)=另一個因數(shù)和被除數(shù)=商×除數(shù)”代入數(shù)據(jù)解答即可.
解答:解:(1)18÷45=0.4,
所以45×0.4=18;
(2)89.1÷11=8.1,
所以11×8.1=89.1;
(3)4.03÷13=0.31,
所以,13×0.31=4.03;
(4)0.56÷0.7=0.8,
所以,0.7×0.8=0.56;
(5)2.1×3=6.3,
所以,6.3÷3=2.1;
(6)1.8×0.7=1.26,
所以,1.26÷0.7=1.8.
故答案為:0.4,8.1,0.31,0.8,6.3,1.26.
點評:本題考查了因數(shù)、因數(shù)和積;被除數(shù)、商、除數(shù)之間關(guān)系的靈活應(yīng)用.