Question

13．把甲倉(cāng)糧食的$\frac{1}{5}$調(diào)入乙倉(cāng)，兩倉(cāng)存糧相等，原來(lái)乙倉(cāng)存糧數(shù)比甲倉(cāng)少（　�。�

• A． $\frac{1}{5}$
• B． $\frac{2}{5}$
• C． $\frac{3}{5}$

Answer 1

分析 甲倉(cāng)原來(lái)存糧當(dāng)作單位“1”，把甲糧倉(cāng)存糧的$\frac{1}{5}$調(diào)入乙倉(cāng)后，根據(jù)分?jǐn)?shù)減法的意義，甲倉(cāng)還剩下全部的1-$\frac{1}{5}$，又此時(shí)兩倉(cāng)存糧相等，則乙倉(cāng)此時(shí)存糧是甲倉(cāng)的1-$\frac{1}{5}$，所以乙倉(cāng)原來(lái)是甲倉(cāng)的1-$\frac{1}{5}$-$\frac{1}{5}$，則原來(lái)乙倉(cāng)比甲倉(cāng)少1-（1-$\frac{1}{5}$-$\frac{1}{5}$）．

解答 解：1-（1-$\frac{1}{5}$-$\frac{1}{5}$）
=1-$\frac{3}{5}$
=$\frac{2}{5}$
答：原來(lái)乙倉(cāng)存糧數(shù)比甲倉(cāng)少$\frac{2}{5}$．
故選：B．

點(diǎn)評(píng) 解答本題的關(guān)鍵是找準(zhǔn)單位“1”，求出乙倉(cāng)此時(shí)存糧是甲倉(cāng)的幾分之幾．