Miscellaneous Exercise

The mean and standard deviation of a group of $100$ observations were found to be $20$ and $3$, respectively. Later on it was found that three observations were incorrect, which were recorded as $21$, $21$ and $18$. Find the mean and standard deviation if the incorrect observations are omitted.

We are given, The total number of observations, $n = 100$. Incorrect mean, $\overline x  = 20$. And, Incorrect standard deviation, $\sigma  = 3$. So, Mean is given by, $\overline {\text{X}}  =...

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The mean and standard deviation of marks obtained by $50$ students of a class in three subjects, Mathematics, Physics and Chemistry are given below. Which of the three subjects shows the highest variability in marks and which shows the lowest?

We are given, The mean and standard deviation of Mathematics are $42$and $12$ respectively. The mean and standard deviation of Physics are $32$ and $15$ respectively. The mean and standard deviation...

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The mean and standard deviation of $20$ observations are found to be $10$ and $2$, respectively. On rechecking, it was found that an observation $8$ was incorrect. Calculate the correct mean and standard deviation in each of the following cases: (i) If wrong item is omitted. (ii) If it is replaced by $12$.

(i) When the wrong item is omitted, We are given, The number of observations, $n = 20$. The mean before rechecking $ = 10$. The standard deviation before rechecking $ = 2$. Mean is given by,...

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Given that ${\overline x}$ is the mean and ${\sigma ^2}$ is the variance of $n$ observations ${x_1}$, ${x_2}$, …., ${x_n}$ . Prove that the mean and variance of the observations $a{x_1}$, $a{x_2}$, $a{x_3}$, …., $a{x_n}$ are $a\overline x $ and ${a^2}{\sigma ^2}$, respectively, ($a \ne 0$).

We are given $n$ observations  ${x_1}$, ${x_2}$, …., ${x_n}$ . Mean of $n$ observations $ = \overline x $. Variance of $n$ observations $ = {\sigma ^2}$. Also, we have variance, $\sigma  = \sqrt...

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