45×7.5-0.45×615等于多少

题目

45×7.5-0.45×615等于多少

答案

0.45×7.5-0.45×615
=0.45×(7.5-615)
=-0.45×607.5
=-(0.5-0.05)×607.5
=-[607.5×0.5-607×0.05]
=-[607.5÷2 - 607.5÷20]
=-[303.75 -30.375]
=-273.375