Question

18．4×[100-x×（1+$\frac{1}{5}$）]=40
x=75．

Answer 1

分析 先化简左边，依据等式的性质，方程两边同时$\frac{24}{5}$x，两边同时减去40，再同时乘$\frac{5}{24}$求解．

解答 解：4×[100-x×（1+$\frac{1}{5}$）]=40
                   4×[100-$\frac{6}{5}$x]=40
                        400-$\frac{24}{5}$x=40
                400-$\frac{24}{5}$x+$\frac{24}{5}$x=40+$\frac{24}{5}$x
                    40+$\frac{24}{5}$x-40=400-40
                               $\frac{24}{5}$x=360
                         $\frac{24}{5}$x×$\frac{5}{24}$=360×$\frac{5}{24}$
                                     x=75
故答案为：75．

点评 此题考查了运用等式的性质解方程，即等式两边同加上或同减去、同乘上或同除以一个数（0除外），两边仍相等，同时注意“=”上下要对齐．