JEE Main & Advanced JEE Main Paper (Held on 10-4-2019 Morning)

  • 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) 3.2

    C) 3.0                              

    D) 2.5

    Correct Answer: A

    Solution :

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


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