Question

11．在□里填上适当的分数
1÷（$\frac{4}{5}$×□-$\frac{1}{5}$ ）=3．

Answer 1

分析 把□看作未知数x，根据等式的性质解方程即可即可．

解答 解：把□看作未知数x，
             1÷（$\frac{4}{5}$×x-$\frac{1}{5}$）=3
1÷（$\frac{4}{5}$×x-$\frac{1}{5}$）×（$\frac{4}{5}$×x-$\frac{1}{5}$）=3×（$\frac{4}{5}$×x-$\frac{1}{5}$）
             3×（$\frac{4}{5}$×x-$\frac{1}{5}$）=1
          3×（$\frac{4}{5}$×x-$\frac{1}{5}$）÷3=1÷3
                    $\frac{4}{5}$×x-$\frac{1}{5}$=$\frac{1}{3}$
                 $\frac{4}{5}$×x-$\frac{1}{5}$+$\frac{1}{5}$=$\frac{1}{3}$+$\frac{1}{5}$
                      $\frac{4}{5}$×x=$\frac{8}{15}$
                   $\frac{4}{5}$×x×$\frac{5}{4}$=$\frac{8}{15}$×$\frac{5}{4}$
                          x=$\frac{2}{3}$
即□=$\frac{2}{3}$．

点评 此题把□看作未知数，依据等式的性质进行求解，注意等号对齐．