Question

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

Answer 1

分析 先化簡左邊，依據(jù)等式的性質(zhì)，方程兩邊同時(shí)$\frac{24}{5}$x，兩邊同時(shí)減去40，再同時(shí)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
故答案為：75．

點(diǎn)評 此題考查了運(yùn)用等式的性質(zhì)解方程，即等式兩邊同加上或同減去、同乘上或同除以一個(gè)數(shù)（0除外），兩邊仍相等，同時(shí)注意“=”上下要對齊．