Given :

Mean $(\bar{x})=\frac{\Sigma x_{i}}{20}=10$

or $\Sigma \mathrm{x}_{\mathrm{i}}=200$ (incorrect)

or $200-25+35=210=\Sigma \mathrm{x}_{\mathrm{i}}$ (Correct)

Now correct $\bar{x}=\frac{210}{20}=10.5$

again given $S . D=2.5(\sigma)$

$\sigma^{2}=\frac{\Sigma \mathrm{x}_{\mathrm{i}}^{2}}{20}-(10)^{2}=(2.5)^{2}$

or $\Sigma \mathrm{x}_{\mathrm{i}}^{2}=2125$ (incorrect)

or $\Sigma \mathrm{x}_{\mathrm{i}}^{2}=2125-25^{2}+35^{2}$ $=2725$ (Correct)

$\therefore$ correct $\sigma^{2}=\frac{2725}{20}-(10.5)^{2}$

$\underline{\underline{\sigma}}^{2}=26$

or $\sigma=26$

$\therefore \underline{\alpha}=10.5, \beta=26$