Question

14．工地上运来沙土$\begin{array}{l}\frac{12}{5}\end{array}$吨，运来的石子是沙土的$\begin{array}{l}\frac{7}{6}\end{array}$，又是石灰的$\begin{array}{l}\frac{14}{15}\end{array}$，工地运来石灰多少吨？

Answer 1

分析 工地上运来沙土$\begin{array}{l}\frac{12}{5}\end{array}$吨，运来的石子是沙土的$\begin{array}{l}\frac{7}{6}\end{array}$，将沙土吨数当作单位“1”，根据分数乘法的意义，运来石子$\begin{array}{l}\frac{12}{5}\end{array}$×$\begin{array}{l}\frac{7}{6}\end{array}$吨，又运来石子是石灰的$\begin{array}{l}\frac{14}{15}\end{array}$，将石灰吨数当作单位“1”，根据分数除法的意义，用石子吨数除以其占石灰吨数的分率，即得工地运来石灰多少吨．

解答 解：$\begin{array}{l}\frac{12}{5}\end{array}$×$\begin{array}{l}\frac{7}{6}\end{array}$÷$\begin{array}{l}\frac{14}{15}\end{array}$
=$\frac{14}{5}$$÷\frac{14}{15}$
=3（吨）
答：工地运来石灰3吨．

点评 求一个数的几分之几是多少，用乘法计算，已知一个数的几分之几是多少，求这个数，用除法计算．