Question

已知 2.45×1.09+0.245×9.1-0.245×10.9-0.0245×91+0.00245×1090+0.000245×9100=b，求 b的值．

Answer 1

分析：因為根據(jù)積不變規(guī)律，兩個數(shù)相乘如果一個數(shù)擴大十倍，另一個數(shù)縮小十倍，他們乘積不變．

解答：解：2.45×1.09+0.245×9.1-0.245×10.9-0.0245×91+0.00245×1090+0.000245×9100
=2.45×1.09+2.45×0.91-2.45×1.09-2.45×0.91+2.45×1.09+2.45×0.91
=2.45×（1.09+0.91-1.09-0.91+1.09+0.91）
=2.45×2
=4.9．

點評：因為兩個數(shù)相乘如果一個數(shù)擴大十倍，另一個數(shù)縮小十倍，他們的乘積不變．