Answer : Option D

Explanation :

Let the areas of the parts be x hectares and (700 - x) hectares.

$MF#%\begin{align}&\text{Difference of the areas of the two parts = x - (700 - x) = 2x - 700}\\\\
&\text{one-fifth of the Average of the two areas = }\dfrac{1}{5}\dfrac{[ x + (700 - x)]}{2}\\
&= \dfrac{1}{5} \times \dfrac{700}{2}= \dfrac{350}{5} = 70\end{align} $MF#%

$MF#%\Rightarrow x = \dfrac{770}{2}= 385$MF#%

Hence, Area of smaller part = (700 - x) = (700 – 385) = 315 hectares.