Question

17．脫式計(jì)算．
$\frac{6}{7}-\frac{5}{14}+\frac{1}{2}$；         $\frac{7}{9}+\frac{2}{3}-\frac{5}{6}$；         $\frac{7}{12}-\frac{1}{3}+\frac{5}{6}$；           $\frac{4}{5}+\frac{1}{2}-\frac{3}{10}$．

Answer 1

分析 異分母分?jǐn)?shù)相加（減），必須先通分，然后按照同分母分?jǐn)?shù)相加（減）的法則進(jìn)行計(jì)算即可．

解答 解：
$\frac{6}{7}-\frac{5}{14}+\frac{1}{2}$
=$\frac{12}{14}$-$\frac{5}{14}$+$\frac{1}{2}$
=$\frac{1}{2}$+$\frac{1}{2}$
=1

$\frac{7}{9}+\frac{2}{3}-\frac{5}{6}$
=$\frac{13}{9}$-$\frac{5}{6}$
=$\frac{11}{18}$

$\frac{7}{12}$-$\frac{1}{3}$+$\frac{5}{6}$
=$\frac{7}{12}$-$\frac{4}{12}$+$\frac{10}{12}$
=$\frac{3}{12}$+$\frac{10}{12}$
=$\frac{13}{12}$

$\frac{4}{5}+\frac{1}{2}-\frac{3}{10}$
=$\frac{8}{10}$+$\frac{5}{10}$-$\frac{3}{10}$
=1．

點(diǎn)評(píng) 此題考查了異分母分?jǐn)?shù)相加減法計(jì)算法則的運(yùn)用．