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Statistics question

2023 · 29 Jan · Shift 1 · Q24
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  5. /2023 · 29 Jan · Shift 1 · Q24

Statistics question

2023 · 29 Jan · Shift 1 · Q24

JEE MainMathematicsStatisticsMCQ+4 / −1
Three rotten apples are mixed accidently with seven good apples and four apples are drawn one by one without replacement. Let the random variable X denote the number of rotten apples. If μ\muμ and σ2\sigma^2σ2 represent mean and variance of X, respectively, then 10(μ2+σ2)10(\mu^2+\sigma^2)10(μ2+σ2) is equal to :
  1. A
    20
  2. B
    30
  3. C
    250
  4. D
    25
View written solutionFree

Correct answer: A

  1. Identify the distribution

There are:

  • 333 rotten apples
  • 777 good apples
  • total 101010 apples

We draw 444 apples without replacement.

If XXX = number of rotten apples drawn, then XXX follows a hypergeometric distribution with parameters: N=10,K=3,n=4N=10,\quad K=3,\quad n=4N=10,K=3,n=4 where:

  • NNN = total population size
  • KKK = number of rotten apples
  • nnn = number of draws

  1. Find the mean μ\muμ

For a hypergeometric random variable, μ=n⋅KN\mu = n\cdot \frac{K}{N}μ=n⋅NK​ So, μ=4⋅310=1210=65\mu = 4\cdot \frac{3}{10} = \frac{12}{10} = \frac{6}{5}μ=4⋅103​=1012​=56​

Thus, μ=65\mu = \frac{6}{5}μ=56​


  1. Find the variance σ2\sigma^2σ2

For a hypergeometric random variable, σ2=n⋅KN(1−KN)⋅N−nN−1\sigma^2 = n\cdot \frac{K}{N}\left(1-\frac{K}{N}\right)\cdot \frac{N-n}{N-1}σ2=n⋅NK​(1−NK​)⋅N−1N−n​ Substitute the values: σ2=4⋅310⋅710⋅10−410−1\sigma^2 = 4\cdot \frac{3}{10}\cdot \frac{7}{10}\cdot \frac{10-4}{10-1}σ2=4⋅103​⋅107​⋅10−110−4​ =4⋅310⋅710⋅69= 4\cdot \frac{3}{10}\cdot \frac{7}{10}\cdot \frac{6}{9}=4⋅103​⋅107​⋅96​ Now simplify: 4⋅310=1210=654\cdot \frac{3}{10} = \frac{12}{10} = \frac{6}{5}4⋅103​=1012​=56​ So, σ2=65⋅710⋅23\sigma^2 = \frac{6}{5}\cdot \frac{7}{10}\cdot \frac{2}{3}σ2=56​⋅107​⋅32​ =4250⋅23=2125⋅23=4275=1425= \frac{42}{50}\cdot \frac{2}{3} = \frac{21}{25}\cdot \frac{2}{3} = \frac{42}{75} = \frac{14}{25}=5042​⋅32​=2521​⋅32​=7542​=2514​

Thus, σ2=1425\sigma^2 = \frac{14}{25}σ2=2514​


  1. Compute μ2+σ2\mu^2 + \sigma^2μ2+σ2

μ2=(65)2=3625\mu^2 = \left(\frac{6}{5}\right)^2 = \frac{36}{25}μ2=(56​)2=2536​ Therefore, μ2+σ2=3625+1425=5025=2\mu^2 + \sigma^2 = \frac{36}{25} + \frac{14}{25} = \frac{50}{25} = 2μ2+σ2=2536​+2514​=2550​=2


  1. Compute the required value

10(μ2+σ2)=10×2=2010(\mu^2+\sigma^2)=10\times 2=2010(μ2+σ2)=10×2=20


  1. Check options

The correct option is: 20\boxed{20}20​ So, Option A is correct.

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