Question

14．工地上運來沙土$\begin{array}{l}\frac{12}{5}\end{array}$噸，運來的石子是沙土的$\begin{array}{l}\frac{7}{6}\end{array}$，又是石灰的$\begin{array}{l}\frac{14}{15}\end{array}$，工地運來石灰多少噸？

Answer 1

分析 工地上運來沙土$\begin{array}{l}\frac{12}{5}\end{array}$噸，運來的石子是沙土的$\begin{array}{l}\frac{7}{6}\end{array}$，將沙土噸數(shù)當(dāng)作單位“1”，根據(jù)分數(shù)乘法的意義，運來石子$\begin{array}{l}\frac{12}{5}\end{array}$×$\begin{array}{l}\frac{7}{6}\end{array}$噸，又運來石子是石灰的$\begin{array}{l}\frac{14}{15}\end{array}$，將石灰噸數(shù)當(dāng)作單位“1”，根據(jù)分數(shù)除法的意義，用石子噸數(shù)除以其占石灰噸數(shù)的分率，即得工地運來石灰多少噸．

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（噸）
答：工地運來石灰3噸．

點評 求一個數(shù)的幾分之幾是多少，用乘法計算，已知一個數(shù)的幾分之幾是多少，求這個數(shù)，用除法計算．