Question

12．能簡(jiǎn)算的要簡(jiǎn)算
$\frac{3}{8}$×$\frac{12}{17}$×$\frac{4}{9}$；    $\frac{3}{5}$×15﹢$\frac{2}{5}$÷$\frac{1}{15}$；    （$\frac{1}{5}$﹢$\frac{3}{8}$）×40；        $\frac{9}{16}$÷（$\frac{3}{8}$﹢$\frac{1}{16}$）．

Answer 1

分析 ①運(yùn)用乘法交換律和結(jié)合律可進(jìn)行簡(jiǎn)便計(jì)算；
②先將“÷$\frac{1}{15}$”化為“×15”，然后運(yùn)用乘法分配律可進(jìn)行簡(jiǎn)便運(yùn)算；
③運(yùn)用乘法分配律可進(jìn)行簡(jiǎn)便運(yùn)算；
④按照四則運(yùn)算法則進(jìn)行計(jì)算即可．

解答 解：①$\frac{3}{8}$×$\frac{12}{17}$×$\frac{4}{9}$
=$\frac{3}{8}$×$\frac{4}{9}$×$\frac{12}{17}$
=$\frac{1}{6}$×$\frac{12}{17}$
=$\frac{2}{17}$

②$\frac{3}{5}$×15﹢$\frac{2}{5}$÷$\frac{1}{15}$
=$\frac{3}{5}$×15﹢$\frac{2}{5}$×15
=（$\frac{3}{5}$+$\frac{2}{5}$）×15
=1×15
=15

③（$\frac{1}{5}$﹢$\frac{3}{8}$）×40
=$\frac{1}{5}$×40+$\frac{3}{8}$×40
=8+15
=23

④$\frac{9}{16}$÷（$\frac{3}{8}$﹢$\frac{1}{16}$）
=$\frac{9}{16}$÷$\frac{7}{16}$
=$\frac{9}{7}$

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．