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Question

The mean and standard deviation of 100 terms are 50 and 3, respectively. The sum of squares of the 100 terms is:

The correct answer is
2,50,900

This problem requires us to find the sum of squares of 100 terms, given their mean and standard deviation. We will use the relationship between mean, standard deviation, and the sum of squares.

Understanding the Given Information

  • Number of terms, n = 100
  • Mean of the terms, $\bar{x}$ = 50
  • Standard deviation of the terms, $\sigma$ = 3

Relevant Statistical Formulas

The formula for the mean ($\bar{x}$) is given by:

$$ \bar{x} = \frac{\sum x}{n} $$

The formula for the variance ($\sigma^2$) is given by:

$$ \sigma^2 = \frac{\sum x^2}{n} - (\bar{x})^2 $$

From this variance formula, we can rearrange it to solve for the sum of squares ($\sum x^2$):

$$ \frac{\sum x^2}{n} = \sigma^2 + (\bar{x})^2 $$ $$ \sum x^2 = n \left( \sigma^2 + (\bar{x})^2 \right) $$

Step-by-Step Calculation

  1. Calculate the variance: Since the standard deviation ($\sigma$) is 3, the variance ($\sigma^2$) is $3^2$. $$ \sigma^2 = 3^2 = 9 $$
  2. Calculate the square of the mean: The mean ($\bar{x}$) is 50, so the square of the mean is $50^2$. $$ (\bar{x})^2 = 50^2 = 2500 $$
  3. Calculate the sum of squares ($\sum x^2$): Using the rearranged variance formula: $$ \sum x^2 = n \left( \sigma^2 + (\bar{x})^2 \right) $$ Substitute the values we have: n = 100, $\sigma^2$ = 9, and $(\bar{x})^2$ = 2500. $$ \sum x^2 = 100 (9 + 2500) $$ $$ \sum x^2 = 100 (2509) $$ $$ \sum x^2 = 250900 $$

Conclusion

The sum of squares of the 100 terms is 2,50,900.

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Important Questions from Standard Deviation

  1. A cold drink bottling plant fills bottles of 500 ml. capacity with mean of 500 ml. and a standard deviation of 5 ml. Atleast what percentage of bottles would contain cold drink between 490 ml. and 510 ml.?

  2. Following are the ages (in years) of 6 people in a group: 25, 30, 35, 40, 45 and 50. What is the standard deviation of their ages (rounded to two decimal places)?
  3. If the mean of a random variable X following Poisson distribution is 3, then standard deviation of the distribution is:

  4. If the standard deviation of a population is 100, then based on a sample of size 100, the standard deviation of sample mean is equal to:

  5. What is the median of 8, 5, 7, 9, 11, 6, 10?

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