Question

12．甲、乙兩數(shù)的和是19.5，取出甲數(shù)的$\frac{1}{6}$給乙數(shù)后，乙數(shù)是甲數(shù)的$\frac{6}{7}$，乙數(shù)原來是6.9．

Answer 1

分析 設(shè)乙數(shù)原來是x，則甲數(shù)為19.5-x，取出甲數(shù)的$\frac{1}{6}$給乙數(shù)后，甲數(shù)還剩甲數(shù)×（1-$\frac{1}{6}$），乙數(shù)變?yōu)橐覕?shù)+甲數(shù)×$\frac{1}{6}$，根據(jù)等量關(guān)系：甲數(shù)×（1-$\frac{1}{6}$）×$\frac{6}{7}$=乙數(shù)+甲數(shù)×$\frac{1}{6}$，列方程解答即可．

解答 解：設(shè)乙數(shù)原來是x，則甲數(shù)為19.5-x，
（19.5-x）×（1-$\frac{1}{6}$）×$\frac{6}{7}$=x+（19.5-x）×$\frac{1}{6}$
               $\frac{195}{14}$-$\frac{5}{7}$x=x+3.25-$\frac{1}{6}$x
               $\frac{195}{14}$-$\frac{5}{7}$x=3.25+$\frac{5}{6}$x
                   $\frac{65}{42}$x=$\frac{299}{28}$
                      x=6.9，
答：乙數(shù)原來是6.9．
故答案為：6.9．

點(diǎn)評(píng) 本題考查了分?jǐn)?shù)除法應(yīng)用題，關(guān)鍵是根據(jù)等量關(guān)系：甲數(shù)×（1-$\frac{1}{6}$）×$\frac{6}{7}$，列=x+甲數(shù)×$\frac{1}{6}$，列方程．