速算必备分小互换

$$\begin{align} &\frac 12 = 50\%\ \ \ \ \ \ \ \ \frac 13 = 33.3\%\ \ \ \ \ \ \ \ \frac 14 = 25\% \\ &\frac 15 = 20\%\ \ \ \ \ \ \ \ \frac 16 = 16.7\%\ \ \ \ \ \ \ \ \frac 17 = 14.3\%\\ &\frac 18 = 12.5\%\ \ \ \ \ \frac 19 = 11.1\%\ \ \ \ \ \ \ \ \frac 23 = 66.7\% \\ &\frac 34 = 75\%\ \ \ \ \ \ \ \ \frac 38 = 37.5\%\ \ \ \ \ \ \ \ \frac 58 = 62.5\% \\ &\frac 27 = 28.6\%\ \ \ \ \ \frac 37 = 42.9\%\ \ \ \ \ \ \ \ \frac 56 = 83.3\% \\ &\frac 29 = 22.2\%\ \ \ \ \ \frac 49 = 44.4\%\ \ \ \ \ \ \ \ \frac n9 = nn.n\% \\ \end{align}$$