If for some x\epsilon 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 : 

 

  • Option 1)

    3.2

  • Option 2)

    3.0

  • Option 3)

    2.5

  • Option 4)

    2.8

 

Answers (1)

Given that total students = 20

So, \sum f_i=20

=> (x+1)^{2}+(2x-5)+x^{2}-3x+x=20

=> x=3,-4

x cannot be -ve 

So, x=3

\bar{x}=\frac{\sum f_i x_i}{\sum f_i}

\bar{x}=\frac{2(x+1)^{2}+3(2x-5)+5(x^{2}-3x)+7x}{20}

Put x=5

\bar{x}=2.8

correct option (4)


Option 1)

3.2

Option 2)

3.0

Option 3)

2.5

Option 4)

2.8

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