两年制学院代数预备课程/附录（步骤）/分数乘法

将分子相乘得到结果的分子。将分母相乘得到结果的分母。然后简化结果。例如，

${\frac {2}{21}}\times {\frac {35}{22}}={\frac {70}{462}}$.

然后我们可以简化

${\frac {70}{462}}={\frac {70{\color {Red}\div 2}}{462{\color {Red}\div 2}}}={\frac {35}{231}}={\frac {35{\color {Red}\div 7}}{231{\color {Red}\div 7}}}={\frac {5}{33}}$.

另一种更简单的乘法方法是先找到分子和分母的质因数，然后简化，最后再相乘。

${\frac {2}{21}}\times {\frac {35}{22}}={\frac {2}{3\cdot 7}}\times {\frac {5\cdot 7}{2\cdot 11}}={\frac {\color {Red}\not {2}}{3\cdot {\color {Blue}\not {7}}}}\times {\frac {5\cdot {\color {Blue}\not {7}}}{{\color {Red}\not {2}}\cdot 11}}={\frac {5}{33}}$.