Question

16．用簡便方法計算：1994$\frac{1}{2}$×79+$\frac{6}{25}$×790+244.9．

Answer 1

分析 首先把分數(shù)化成小數(shù)，1994.5×79+0.24×790+244.9，再根據(jù)因數(shù)與積的變化規(guī)律將原式轉(zhuǎn)化為：199.45×790+0.24×790+244.9，運用乘法分配律簡算．

解答 解：1994$\frac{1}{2}$×79+$\frac{6}{25}$×790+244.9
=1994.5×79+0.24×790+244.9
=199.45×790+0.24×790+244.9
=（199.45+0.24）×790+244.9
=199.69×790+244.9
=（200-0.31）×790+244.9
=200×790-0.31×790+244.9
=158000-244.9+244.9
=158000．

點評 此題考查的目的是理解掌握分數(shù)化成小數(shù)的方法、因數(shù)與積的變化規(guī)律、乘法分配律的意義，并且能夠靈活運用因數(shù)與積的變化規(guī)律和乘法分配律進行簡便計算．