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Statistics question

2024 · 30 Jan · Shift 2 · Q56
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Statistics question

2024 · 30 Jan · Shift 2 · Q56

JEE MainMathematicsStatisticsNumerical+4 / −1

The variance σ2\sigma^2σ2 of the data

xix_ixi​ 0 1 5 6 10 12 17
fif_ifi​ 3 2 3 2 6 3 3

is ‾\underline{\hspace{2cm}}​.

Numerical answer
View written solutionFree

Correct answer: \(\DFRAC{320}{11}\)

  1. Given data

The values are: xi:0,1,5,6,10,12,17x_i: 0,1,5,6,10,12,17xi​:0,1,5,6,10,12,17 with corresponding frequencies fi:3,2,3,2,6,3,3f_i: 3,2,3,2,6,3,3fi​:3,2,3,2,6,3,3

We use the variance formula for a frequency distribution: σ2=∑fi(xi−xˉ)2∑fi\sigma^2=\frac{\sum f_i(x_i-\bar{x})^2}{\sum f_i}σ2=∑fi​∑fi​(xi​−xˉ)2​ where xˉ=∑fixi∑fi\bar{x}=\frac{\sum f_ix_i}{\sum f_i}xˉ=∑fi​∑fi​xi​​


  1. Find total frequency

N=∑fi=3+2+3+2+6+3+3=22N=\sum f_i=3+2+3+2+6+3+3=22N=∑fi​=3+2+3+2+6+3+3=22


  1. Find the mean

Compute ∑fixi\sum f_i x_i∑fi​xi​:

∑fixi=3(0)+2(1)+3(5)+2(6)+6(10)+3(12)+3(17)\sum f_i x_i=3(0)+2(1)+3(5)+2(6)+6(10)+3(12)+3(17)∑fi​xi​=3(0)+2(1)+3(5)+2(6)+6(10)+3(12)+3(17)

=0+2+15+12+60+36+51=176=0+2+15+12+60+36+51=176=0+2+15+12+60+36+51=176

Hence, xˉ=17622=8\bar{x}=\frac{176}{22}=8xˉ=22176​=8


  1. Compute ∑fi(xi−xˉ)2\sum f_i (x_i-\bar{x})^2∑fi​(xi​−xˉ)2

Since xˉ=8\bar{x}=8xˉ=8,

∑fi(xi−8)2\sum f_i(x_i-8)^2∑fi​(xi​−8)2

Now calculate term by term:

  • For x=0x=0x=0, f=3f=3f=3: 3(0−8)2=3(64)=1923(0-8)^2=3(64)=1923(0−8)2=3(64)=192
  • For x=1x=1x=1, f=2f=2f=2: 2(1−8)2=2(49)=982(1-8)^2=2(49)=982(1−8)2=2(49)=98
  • For x=5x=5x=5, f=3f=3f=3: 3(5−8)2=3(9)=273(5-8)^2=3(9)=273(5−8)2=3(9)=27
  • For x=6x=6x=6, f=2f=2f=2: 2(6−8)2=2(4)=82(6-8)^2=2(4)=82(6−8)2=2(4)=8
  • For x=10x=10x=10, f=6f=6f=6: 6(10−8)2=6(4)=246(10-8)^2=6(4)=246(10−8)2=6(4)=24
  • For x=12x=12x=12, f=3f=3f=3: 3(12−8)2=3(16)=483(12-8)^2=3(16)=483(12−8)2=3(16)=48
  • For x=17x=17x=17, f=3f=3f=3: 3(17−8)2=3(81)=2433(17-8)^2=3(81)=2433(17−8)2=3(81)=243

Adding: 192+98+27+8+24+48+243=640192+98+27+8+24+48+243=640192+98+27+8+24+48+243=640


  1. Find the variance

σ2=64022=32011≈29.09\sigma^2=\frac{640}{22}=\frac{320}{11}\approx 29.09σ2=22640​=11320​≈29.09

Since this is an integer-type question, the exact variance is: 32011\boxed{\frac{320}{11}}11320​​

If the question expects the nearest integer, it is 292929.


  1. Compare with stored answer

Stored correct answer: 292929

Our computed variance is σ2=32011≈29.09\sigma^2=\frac{320}{11}\approx 29.09σ2=11320​≈29.09 So the exact answer is not exactly 292929, but its approximate value is 292929.

Therefore, I do not fully agree with the stored answer if exact variance is required.

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