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例1:小新、爸爸和妈妈一起吃一个蛋糕,每人吃$\frac {2}{9}$个,3人一共吃多少个?
解析:$\frac {2}{9}×3= \frac {2×3}{9}= \frac {6}{9}= \frac {2}{3}$
解析:$\frac {2}{9}×3= \frac {2×3}{9}= \frac {6}{9}= \frac {2}{3}$
答案
$\frac{2}{3}$个
变式训练1:想一想,填一填。
$\frac {5}{8}+\frac {5}{8}+\frac {5}{8}+\frac {5}{8}= ()×()$
$\frac {2}{7}×4= \frac {()×()}{()}= \frac {()}{()}$
$\frac {5}{8}+\frac {5}{8}+\frac {5}{8}+\frac {5}{8}= ()×()$
$\frac {2}{7}×4= \frac {()×()}{()}= \frac {()}{()}$
答案
$\frac {5}{8}×4$ 2 4 7 8 7
例2:列式计算。
(1)$\frac {5}{12}公顷的\frac {4}{7}$是多少? (2)$\frac {2}{3}分米的\frac {4}{5}$是多少分米?
解析:$\frac {5}{12}×\frac {4}{7}= \frac {5×4}{12×7}= \frac {5}{21}$(公顷) 解析:$\frac {2}{3}×\frac {4}{5}= \frac {2}{3}×\frac {4}{5}= \frac {8}{15}$(分米)
(1)$\frac {5}{12}公顷的\frac {4}{7}$是多少? (2)$\frac {2}{3}分米的\frac {4}{5}$是多少分米?
解析:$\frac {5}{12}×\frac {4}{7}= \frac {5×4}{12×7}= \frac {5}{21}$(公顷) 解析:$\frac {2}{3}×\frac {4}{5}= \frac {2}{3}×\frac {4}{5}= \frac {8}{15}$(分米)
答案
（1）$\frac{5}{12}$公顷的$\frac{4}{7}$是$\frac{5}{21}$公顷；（2）$\frac{2}{3}$分米的$\frac{4}{5}$是$\frac{8}{15}$分米。
例4:$4.8×(\frac {1}{6}-\frac {1}{12})$
解析:因为$4.8= \frac {48}{10}= \frac {24}{5}$
$=\frac {24}{5}×(\frac {1}{6}-\frac {1}{12})$
$=\frac {24}{5}×\frac {1}{6}-\frac {24}{5}×\frac {1}{12}$
$=\frac {4}{5}-\frac {2}{5}$
$=\frac {2}{5}$
解析:因为$4.8= \frac {48}{10}= \frac {24}{5}$
$=\frac {24}{5}×(\frac {1}{6}-\frac {1}{12})$
$=\frac {24}{5}×\frac {1}{6}-\frac {24}{5}×\frac {1}{12}$
$=\frac {4}{5}-\frac {2}{5}$
$=\frac {2}{5}$
答案
$\frac{2}{5}$
