Question

19．計算下列各題．

100×$\frac{2}{5}$×$\frac{1}{8}$	15×$\frac{1}{5}$÷5	3÷$\frac{3}{40}$×$\frac{3}{5}$
$\frac{7}{10}$×$\frac{5}{16}$÷$\frac{21}{32}$	$\frac{8}{5}$÷$\frac{7}{20}$÷4	$\frac{5}{9}$÷$\frac{5}{4}$÷$\frac{4}{5}$．

Answer 1

分析 把除法化成乘法后直接約分求解即可．

解答 解：（1）100×$\frac{2}{5}$×$\frac{1}{8}$
=$\frac{100×2×1}{5×8}$
=5；

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

（3）3÷$\frac{3}{40}$×$\frac{3}{5}$  
=3×$\frac{40}{3}$×$\frac{3}{5}$  
=$\frac{3×40×3}{3×5}$
=24；

（4）$\frac{7}{10}$×$\frac{5}{16}$÷$\frac{21}{32}$
=$\frac{7}{10}$×$\frac{5}{16}$×$\frac{32}{21}$
=$\frac{7×5×32}{10×16×21}$
=$\frac{1}{3}$；

（5）$\frac{8}{5}$÷$\frac{7}{20}$÷4
=$\frac{8}{5}$×$\frac{20}{7}×\frac{1}{4}$
=$\frac{8×20×1}{5×7×4}$
=$\frac{8}{7}$；

（6）$\frac{5}{9}$÷$\frac{5}{4}$÷$\frac{4}{5}$
=$\frac{5}{9}$×$\frac{4}{5}×\frac{5}{4}$
=$\frac{5×4×5}{9×5×4}$
=$\frac{5}{9}$．

點評 本題是根據(jù)運算的法則直接求解，注意把結(jié)果化成最簡分數(shù)即可．