兩年制學院代數預備課程/附錄（步驟）/分數乘法

將分子相乘得到結果的分子。將分母相乘得到結果的分母。然後簡化結果。例如，

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

然後我們可以簡化

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

另一種更簡單的乘法方法是先找到分子和分母的質因數，然後簡化，最後再相乘。

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