Question

7．校園里楊樹(shù)的棵數(shù)是松樹(shù)的$\frac{2}{3}$，柳樹(shù)的棵數(shù)是松樹(shù)的$\frac{2}{5}$．已知楊樹(shù)的有20棵，柳樹(shù)有多少棵？

Answer 1

分析 楊樹(shù)的棵數(shù)是松樹(shù)的$\frac{2}{3}$，已知楊樹(shù)的有20棵，將松樹(shù)棵數(shù)當(dāng)作單位“1”，根據(jù)分?jǐn)?shù)除法的意義，松樹(shù)有20$÷\frac{2}{3}$棵，又柳樹(shù)的棵數(shù)是松樹(shù)的$\frac{2}{5}$，根據(jù)分?jǐn)?shù)乘法的意義，用松樹(shù)棵數(shù)乘楊樹(shù)占松樹(shù)棵數(shù)的分率，即得柳樹(shù)多少棵．

解答 解：20$÷\frac{2}{3}$×$\frac{2}{5}$
=30×$\frac{2}{5}$
=12（棵）
答：柳樹(shù)有12棵．

點(diǎn)評(píng) 已知一個(gè)數(shù)的幾分之幾是多少，求這個(gè)數(shù)，用除法．求一個(gè)數(shù)的幾分之幾是多少，用乘法．