If mean and variance of following data: 6,10,7,13, a, 12, b, 12 are 9 and frac{37}{4} respectively,

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13.Statistics

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If the mean and variance of the following data:

$6,10,7,13, a, 12, b, 12$ are 9 and $\frac{37}{4}$ respectively, then $(a-b)^{2}$ is equal to:

$12$

$24$

$16$

$32$

(JEE MAIN-2021)

Solution

$\text { Mean }=\frac{6+10+7+13+a+12+b+12}{8}=9$

$60+a+b=72$

$a+b=12$

$\text { veriance }=\frac{\sum x_{i}^{2}}{n}-\left(\frac{\sum x_{i}}{n}\right)=\frac{37}{4}$

$\sum x_{i}^{2}=6^{2}+10^{2}+7^{2}+13^{2}+a^{2}+b^{2}+12^{2}+12^{2}$

$=a^{2}+b^{2}+642$

$\frac{a^{2}+b^{2}+642}{8}-(9)^{2}=\frac{37}{4}$

$\frac{a^{2}+b^{2}}{8}+\frac{321}{4}-81=\frac{37}{4}$

$\frac{a^{2}+b^{2}}{8}=81+\frac{37}{4}-\frac{321}{4}$

$\frac{a^{2}+b^{2}}{8}=81-71$

$\therefore a^{2}+b^{2}=80$

From $(1)$ $a^{2}+b^{2}+2 a b=144$

$80+2 a b=144 \therefore 2 a b=64$

$(a-b)^{2}=a^{2}+b^{2}-2 a b=80-64=16$

Standard 11

Mathematics

Find the mean and variance for the data

${x_i}$ $92$ $93$ $97$ $98$ $102$ $104$ $109$

${f_i}$ $3$ $2$ $3$ $2$ $6$ $3$ $3$

hard

Mean of $5$ observations is $7.$ If four of these observations are $6, 7, 8, 10$ and one is missing then the variance of all the five observations is

medium

(JEE MAIN-2013)

The data is obtained in tabular form as follows.

${x_i}$ $60$ $61$ $62$ $63$ $64$ $65$ $66$ $67$ $68$

${f_i}$ $2$ $1$ $12$ $29$ $25$ $12$ $10$ $4$ $5$

hard

Let the mean and variance of four numbers $3,7, x$ and $y(x>y)$ be $5$ and $10$ respectively. Then the mean of four numbers $3+2 \mathrm{x}, 7+2 \mathrm{y}, \mathrm{x}+\mathrm{y}$ and $x-y$ is ….. .

hard

(JEE MAIN-2021)

If $x_1, x_2,…..x_n$ are $n$ observations such that $\sum\limits_{i = 1}^n {x_i^2} = 400$ and $\sum\limits_{i = 1}^n {{x_i}} = 100$ , then possible value of $n$ among the following is

normal

${x_i}$	$92$	$93$	$97$	$98$	$102$	$104$	$109$
${f_i}$	$3$	$2$	$3$	$2$	$6$	$3$	$3$

${x_i}$	$60$	$61$	$62$	$63$	$64$	$65$	$66$	$67$	$68$
${f_i}$	$2$	$1$	$12$	$29$	$25$	$12$	$10$	$4$	$5$

If the mean and variance of the following data: $6,10,7,13, a, 12, b, 12$ are 9 and $\frac{37}{4}$ respectively, then $(a-b)^{2}$ is equal to:

Solution

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If the mean and variance of the following data:

$6,10,7,13, a, 12, b, 12$ are 9 and $\frac{37}{4}$ respectively, then $(a-b)^{2}$ is equal to:

Find the mean and variance for the data

${x_i}$ $92$ $93$ $97$ $98$ $102$ $104$ $109$

${f_i}$ $3$ $2$ $3$ $2$ $6$ $3$ $3$

The data is obtained in tabular form as follows.

${x_i}$ $60$ $61$ $62$ $63$ $64$ $65$ $66$ $67$ $68$

${f_i}$ $2$ $1$ $12$ $29$ $25$ $12$ $10$ $4$ $5$