• # question_answer If for some $x\in R,$the frequency distribution of the marks obtained by 20 students in a test is: Marks 2 3 5 7 Frequency ${{(x+1)}^{2}}$ $2x-5$ ${{x}^{2}}-3x$ $x$ then the mean of the marks is : [JEE Main 10-4-2019 Morning] A) 2.8      B) 3.2C) 3.0                              D) 2.5

$\sum\limits_{{}}^{{}}{{{f}_{i}}}=20=2{{x}^{2}}+2x-4$           $\Rightarrow {{x}^{2}}+2x-24=0$ $x=3,-4$(rejected) $\bar{x}=\frac{\sum\limits_{{}}^{{}}{{{x}_{i}}{{f}_{i}}}}{\sum\limits_{{}}^{{}}{{{f}_{i}}}}=2.8$