Question

3．計算下面各題，能簡算的要簡算．
 （$\frac{3}{4}$-$\frac{1}{8}$）÷$\frac{5}{12}$     
 $\frac{8}{13}$÷7+$\frac{1}{7}$×$\frac{5}{13}$
$\frac{5}{6}$÷$\frac{8}{9}$÷$\frac{1}{3}$
$\frac{1}{5}$×8$÷\frac{4}{5}$．

Answer 1

分析 ①先算減法，再算除法．
②用乘法分配律計算．
③把除法變成乘法，先約分再計算．
④把除法變成乘法，先約分再計算．

解答 解：①（$\frac{3}{4}$-$\frac{1}{8}$）÷$\frac{5}{12}$   
=$\frac{5}{8}×\frac{12}{5}$
=$\frac{3}{2}$

②$\frac{8}{13}$÷7+$\frac{1}{7}$×$\frac{5}{13}$
=（$\frac{8}{13}+\frac{5}{13}$）×$\frac{1}{7}$
=$1×\frac{1}{7}$
=$\frac{1}{7}$

③$\frac{5}{6}$÷$\frac{8}{9}$÷$\frac{1}{3}$
=$\frac{5}{6}×\frac{9}{8}×\frac{3}{1}$
=$\frac{45}{16}$

④$\frac{1}{5}$×8$÷\frac{4}{5}$
=$\frac{1}{5}×8×\frac{5}{4}$
=2

點(diǎn)評 本題主要考查分?jǐn)?shù)四則混合運(yùn)算的計算順序．