1. If for some x E R, the frequency distribution of the marks obtained by 20 students in a test is :

$\sum \mathrm{f}_{\mathrm{i}}=20=2 \mathrm{x}^{2}+2 \mathrm{x}-4$

$\Rightarrow \mathrm{x}^{2}+2 \mathrm{x}-24=0$

$\mathrm{x}=3,-4$ (rejected)

$\overline{\mathrm{x}}=\frac{\sum \mathrm{x}_{\mathrm{i}} f_{\mathrm{i}}}{\sum f_{\mathrm{i}}}=2.8$