According to the question

we know the formula,

Mean(Avg)=$\frac{\mathrm{Sum} \mathrm{of} \mathrm{observations} \left(\mathrm{S}\right)}{\mathrm{Number} \mathrm{of} \mathrm{observations} \left(\mathrm{N}\right)}$

Given, Mean (Avg)= 31, N= 20

 $$\begin{gathered} 31=\frac{\mathrm{S}}{20} \\ \mathrm{S}=20\times 31=620 \end{gathered}$$

But an observation was taken as 52 instead of 27

= 52-25=27

∴ The correct mean of 20 observations is

 $$\begin{gathered} =\frac{\mathrm{S}-27}{\mathrm{N}} \\ =\frac{620-27}{20} \\ =\frac{593}{20}=29.65 \end{gathered}$$

Hence, Option D is correct.