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NCERT Exemplar · Q18
Q.

Determine the mean and standard deviation for the following distribution:

Marks2345678910111213141516
Frequency166882230210001
Mizoram MbseLong· 5mImportance★★★★★est
69% · 62/90 Questions
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The mean of the given frequency distribution is calculated by summing the products of marks and frequencies and dividing by the total frequency. The standard deviation is found using the formula involving the sum of squared marks weighted by frequencies. The mean is 5.975\boxed{5.975} and the standard deviation is approximately 2.850\boxed{2.850}.

To determine the mean and standard deviation for a frequency distribution, we need to understand what these measures represent. The mean (xˉ\bar{x}) is the average value of the data, taking into account how often each value appears. It's the central point around which the data balances. The standard deviation (σ\sigma) measures the typical spread or dispersion of the data points around this mean. A small standard deviation indicates data points are clustered closely around the mean, while a large standard deviation means they are more spread out.

For a frequency distribution where xix_i represents the individual data points (marks) and fif_i represents their corresponding frequencies, the formulas are:

Mean: xˉ=∑i=1nfixi∑i=1nfi\bar{x} = \frac{\sum_{i=1}^{n} f_i x_i}{\sum_{i=1}^{n} f_i}

Standard Deviation: σ=∑i=1nfixi2∑i=1nfi−(∑i=1nfixi∑i=1nfi)2\sigma = \sqrt{\frac{\sum_{i=1}^{n} f_i x_i^2}{\sum_{i=1}^{n} f_i} - \left(\frac{\sum_{i=1}^{n} f_i x_i}{\sum_{i=1}^{n} f_i}\right)^2}

This formula is often written as σ=∑fixi2N−xˉ2\sigma = \sqrt{\frac{\sum f_i x_i^2}{N} - \bar{x}^2}, where N=∑fiN = \sum f_i is the total frequency.

Let's calculate these values step-by-step.

  1. Organize the data and calculate necessary sums.

    To efficiently calculate the mean and standard deviation, we create an extended table. This table includes columns for the marks (xix_i), frequencies (fif_i), the product fixif_i x_i, the square of the marks xi2x_i^2, and the product fixi2f_i x_i^2. The sums of the fif_i, fixif_i x_i, and fixi2f_i x_i^2 columns are essential for our formulas.

    Marks (xix_i)Frequency (fif_i)fixif_i x_ixi2x_i^2fixi2f_i x_i^2
    21244
    3618954
    46241696
    584025200
    684836288
    72144998
    821664128
    932781243
    10001000
    11222121242
    12112144144
    13001690
    14001960
    15002250
    16116256256
    Total∑fi=40\sum f_i = 40∑fixi=239\sum f_i x_i = 239∑fixi2=1753\sum f_i x_i^2 = 1753

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