Question

6．用梯等式計(jì)算．
?[2.5-（$\frac{17}{20}$+0.15）×0.6]×$\frac{2}{5}$；                   $\frac{19}{25}$×（7.2×$\frac{4}{5}$）-$\frac{17}{25}$×$\frac{1}{8}$?

Answer 1

分析 ①先計(jì)算中括號(hào)內(nèi)部的小括號(hào)里面的加法，然后再計(jì)算中括號(hào)內(nèi)部的，再計(jì)算括號(hào)外面的乘法．
②把括號(hào)去掉，把分?jǐn)?shù)化成小數(shù)，然后再運(yùn)用小數(shù)乘法及減法的計(jì)算法則進(jìn)行計(jì)算即可．

解答 解：①[2.5-（$\frac{17}{20}$+0.15）×0.6]×$\frac{2}{5}$
=[2.5-（$\frac{17}{20}$+$\frac{3}{20}$）×$\frac{3}{5}$]×$\frac{2}{5}$
=[2.5-0.6]×0.4
=1.9×0.4
=0.76

②$\frac{19}{25}$×（7.2×$\frac{4}{5}$）-$\frac{17}{25}$×$\frac{1}{8}$
=$\frac{19}{25}$×7.2×$\frac{4}{5}$-$\frac{17}{25}$×$\frac{1}{8}$
=0.76×7.2×0.8-0.68×0.125
=0.608-0.085
=0.523

點(diǎn)評(píng) 考查了運(yùn)算定律與簡(jiǎn)便運(yùn)算，四則混合運(yùn)算．注意運(yùn)算順序和運(yùn)算法則，靈活運(yùn)用所學(xué)的運(yùn)算律簡(jiǎn)便計(jì)算．