Question

17．計(jì)算：$\frac{5}{21}$×$\frac{2}{7}$+2$\frac{19}{21}$×$\frac{5}{7}$+（1-$\frac{3}{7}$）．

Answer 1

分析 把算式中的$\frac{5}{21}$×$\frac{2}{7}$+2$\frac{19}{21}$×$\frac{5}{7}$轉(zhuǎn)化成$\frac{5}{21}$×$\frac{2}{7}$+$\frac{5}{21}$×$\frac{61}{7}$運(yùn)用乘法的分配律進(jìn)行計(jì)算即可．

解答 解：$\frac{5}{21}$×$\frac{2}{7}$+2$\frac{19}{21}$×$\frac{5}{7}$+（1-$\frac{3}{7}$）
=$\frac{5}{21}$×$\frac{2}{7}$+$\frac{61}{21}$×$\frac{5}{7}$+$\frac{4}{7}$
=$\frac{5}{21}$×$\frac{2}{7}$+$\frac{5}{21}$×$\frac{61}{7}$+$\frac{4}{7}$
=$\frac{5}{21}$×（$\frac{2}{7}+\frac{61}{7}$）$+\frac{4}{7}$
=$\frac{5}{21}×9$$+\frac{4}{7}$
=$\frac{15}{7}+\frac{4}{7}$
=$\frac{19}{7}$

點(diǎn)評(píng) 本題考查了學(xué)生通過乘法的分配律進(jìn)行計(jì)算，體驗(yàn)計(jì)算的簡(jiǎn)便．