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Statistics question

2021 · 25 Jul · Shift 1 · Q39
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  5. /2021 · 25 Jul · Shift 1 · Q39

Statistics question

2021 · 25 Jul · Shift 1 · Q39

JEE MainMathematicsStatisticsNumerical+4 / −1
Consider the following frequency distribution :

Class : 10-20 20-30 30-40 40-50 50-60
Frequency : α\alphaα 110 54 30 β\betaβ


If the sum of all frequencies is 584 and median is 45, then | α−β\alpha-\betaα−β | is equal to ‾\underline{\hspace{2cm}}​.
Numerical answer
View written solutionFree

Correct answer: 164

  1. Given frequency table

[ \begin{array}{c|ccccc} \text{Class} & 10-20 & 20-30 & 30-40 & 40-50 & 50-60 \ \hline \text{Frequency} & \alpha & 110 & 54 & 30 & \beta \end{array} ]

Total frequency is given as [ \alpha+110+54+30+\beta=584 ] so [ \alpha+\beta+194=584 ] [ \alpha+\beta=390 \qquad ...(1) ]

  1. Use the median formula

Total number of observations: [ N=584 ] Hence, [ \frac{N}{2}=292 ]

Given median is 454545.

The median class is clearly 40−5040-5040−50, because median value 454545 lies in this class.

For grouped data, [ \text{Median}=l+\left(\frac{\frac{N}{2}-c_f}{f}\right)h ] where:

  • l=40l=40l=40 (lower limit of median class),
  • h=10h=10h=10,
  • f=30f=30f=30 (frequency of median class),
  • cf=α+110+54=α+164c_f=\alpha+110+54=\alpha+164cf​=α+110+54=α+164.

Substitute in the formula: [ 45=40+\left(\frac{292-(\alpha+164)}{30}\right)10 ]

Simplify: [ 5=\left(\frac{128-\alpha}{30}\right)10 ] [ 5=\frac{128-\alpha}{3} ] [ 15=128-\alpha ] [ \alpha=113 ]

  1. Find β\betaβ using (1)

[ \alpha+\beta=390 ] [ 113+\beta=390 ] [ \beta=277 ]

  1. Compute ∣α−β∣|\alpha-\beta|∣α−β∣

[ |\alpha-\beta|=|113-277|=164 ]

  1. Final Answer

[ \boxed{164} ]

The derived answer matches the stored correct answer.

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