Math Problem Statement

The mean and sample standard deviation of the dataset consisting of 9 observations is 14 and 10 respectively. Later it is noted that one observation 11 is wrongly noted as 6. What is the sample variance of the original dataset? (Correct to 2 decimal place accuracy)

Solution

To find the sample variance of the original dataset, we need to correct the mistakenly recorded value and then recalculate the variance.

Given:

  • Mean (xˉ\bar{x}) of the dataset: 14
  • Sample standard deviation (s): 10
  • Number of observations (n): 9
  • Incorrect value: 6 (should be 11)

First, let's determine the sum of the original dataset using the mean: xˉ=xin    xi=xˉ×n=14×9=126\bar{x} = \frac{\sum x_i}{n} \implies \sum x_i = \bar{x} \times n = 14 \times 9 = 126

Now, let's find the sum of squares of the original dataset using the variance formula: s2=1n1i=1n(xixˉ)2    i=1n(xixˉ)2=s2×(n1)=102×8=800s^2 = \frac{1}{n-1} \sum_{i=1}^{n} (x_i - \bar{x})^2 \implies \sum_{i=1}^{n} (x_i - \bar{x})^2 = s^2 \times (n-1) = 10^2 \times 8 = 800

Next, we need to adjust this sum of squares to account for the incorrect value: Original sum of squares=i=19xi2\text{Original sum of squares} = \sum_{i=1}^{9} x_i^2

The incorrect dataset sum of squares can be expressed as: i=19xi2=800+nxˉ2=800+9142=800+1764=2564\sum_{i=1}^{9} x_i^2 = 800 + n \cdot \bar{x}^2 = 800 + 9 \cdot 14^2 = 800 + 1764 = 2564

Identify and correct the contribution of the incorrect value:

  • Incorrect value: 6
  • Correct value: 11

The difference in the squares due to the correction is: 11262=12136=8511^2 - 6^2 = 121 - 36 = 85

The corrected sum of squares: Corrected sum of squares=2564+85=2649\text{Corrected sum of squares} = 2564 + 85 = 2649

Recalculate the sample variance with the corrected sum of squares: s2=1n1i=1n(xi2)=26491262/98=264917648=8858=110.625s^2 = \frac{1}{n-1} \sum_{i=1}^{n} (x_i^2) = \frac{2649 - 126^2 / 9}{8} = \frac{2649 - 1764}{8} = \frac{885}{8} = 110.625

Thus, the sample variance of the original dataset, corrected to two decimal places, is: 110.63110.63

Would you like further details or have any questions? Here are some related questions you might find useful:

  1. How do you calculate the sample mean from a dataset?
  2. What is the difference between sample variance and population variance?
  3. How do you find the sum of squares in a dataset?
  4. What steps are involved in correcting a dataset with an error?
  5. How do changes in individual data points affect the overall variance?

Tip: Always double-check your dataset for accuracy before performing statistical calculations to ensure valid results.

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Math Problem Analysis

Mathematical Concepts

Statistics
Sample Variance
Standard Deviation

Formulas

Sample Variance Formula
Standard Deviation Formula

Theorems

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Suitable Grade Level

Advanced High School