Question

15．計算：
$\frac{6}{21}×\frac{7}{9}$=
$\frac{8}{3}$×$\frac{5}{4}$=
$\frac{7}{4}$×$\frac{5}{6}$=
$\frac{7}{5}$×$\frac{4}{5}$=
$\frac{4}{9}$×$\frac{5}{11}$=
$\frac{2}{3}$×$\frac{4}{7}$=
$\frac{14}{15}$×$\frac{5}{28}$=
$\frac{4}{9}$×$\frac{8}{3}$=
$\frac{3}{5}$×$\frac{5}{9}$=
$\frac{21}{25}$÷7=
$\frac{12}{13}$÷6=
$\frac{5}{7}$÷$\frac{10}{21}$=
$\frac{1}{6}$÷$\frac{4}{9}$=
4÷$\frac{5}{6}$=
$\frac{5}{8}$÷$\frac{2}{3}$=

Answer 1

分析 根據(jù)分數(shù)乘法、除法的計算法則，分數(shù)乘法，分子相乘的積作分子，分母相乘的積作分母，能約分先約分計算簡便；分數(shù)除法，首先把除數(shù)轉化為乘它的倒數(shù)，再根據(jù)分數(shù)乘法的計算法則計算．

解答 解：計算：
$\frac{6}{21}×\frac{7}{9}$=$\frac{2}{9}$
$\frac{8}{3}$×$\frac{5}{4}$=$\frac{10}{3}$
$\frac{7}{4}$×$\frac{5}{6}$=$\frac{35}{24}$
$\frac{7}{5}$×$\frac{4}{5}$=$\frac{28}{25}$
$\frac{4}{9}$×$\frac{5}{11}$=$\frac{20}{99}$
$\frac{2}{3}$×$\frac{4}{7}$=$\frac{8}{21}$
$\frac{14}{15}$×$\frac{5}{28}$=$\frac{1}{6}$
$\frac{4}{9}$×$\frac{8}{3}$=$\frac{32}{27}$
$\frac{3}{5}$×$\frac{5}{9}$=$\frac{1}{3}$
$\frac{21}{25}$÷7=$\frac{21}{25}×\frac{1}{7}=\frac{3}{25}$
$\frac{12}{13}$÷6=$\frac{12}{13}×\frac{1}{6}=\frac{2}{13}$
$\frac{5}{7}$÷$\frac{10}{21}$=$\frac{5}{7}×\frac{21}{10}$=$\frac{3}{2}$
$\frac{1}{6}$÷$\frac{4}{9}$=$\frac{1}{6}×\frac{9}{4}$=$\frac{3}{8}$
4÷$\frac{5}{6}$=4×$\frac{6}{5}$=$\frac{24}{5}$
$\frac{5}{8}$÷$\frac{2}{3}$=$\frac{5}{6}×\frac{3}{2}$=$\frac{5}{4}$．

點評 此題考查的目的是理解掌握分數(shù)乘法、除法的計算法則，并且能夠正確熟練地進行計算．