Evaluate $\frac{0.42\div 2.5}{0.5\times 2.05}$ leaving the answer in standard form
$1.629\times {{10}^{2}}$
$1.6639\times {{10}^{1}}$
$1.639\times {{10}^{-1}}$
$1.639\times {{10}^{-2}}$
$\begin{align} & \frac{0.42\div 2.5}{0.5\times 2.05}=\frac{\tfrac{42}{100}\div \tfrac{25}{10}}{\tfrac{5}{10}\times \tfrac{205}{100}}=\frac{\tfrac{42}{100}\times \tfrac{10}{25}}{\tfrac{5}{10}\times \tfrac{205}{100}} \\ & \frac{0.42\div 2.5}{0.5\times 2.05}=\left( \frac{42}{100}\times \frac{10}{25} \right)\div \left( \frac{5}{10}\times \frac{205}{100} \right) \\ & \frac{0.42\div 2.5}{0.5\times 2.05}=\frac{42}{100}\times \frac{10}{25}\times \frac{10}{5}\times \frac{100}{205}=\text{0}\text{.1639} \\ & \frac{0.42\div 2.5}{0.5\times 2.05}\text{=1}\text{.639}\times \text{1}{{\text{0}}^{-1}} \\\end{align}$