Question

if the mean of the following 9 numbers is 11 if 8 of them are given as 7, 12, 9, 14, 21, 3, 8, 15 then find the ninth number​

Answer 1

Answer:

the answer below is wrong. the addition below is wrong.

Step-by-step explanation:

let the 9th number be x.

9 = 7,12,9,14,21,3,8,15,x/11

9 x 11 = 89 + x

99 = 89+x

x = 89 - 99

∴ x = 10

Answer 2

The ninth number is 10.

Given,

The mean of the following 9 numbers is 11. 8 of them are given as 7, 12, 9, 14, 21, 3, 8, 15.

To Find,

The ninth number =?

Solution,

We can solve the question as follows:

It is given that the mean of 9 numbers is 11. 8 of the numbers are: 7, 12, 9, 14, 21, 3, 8, 15. We have to find the ninth number.

$Mean\: of\: 9\: numbers = 11$

Let the ninth number be equal to x.

The formula for finding the mean of a set of observations is given as:

$Mean = \frac{Sum\: of\: all\: observations}{Total\: observations}$

In the given question,

$Sum\: of\: all\: observations = 7 + 12 + 9 +14+21+3+8+15+x = 89 + x$

$Total\: observations = 9$

Substituting the values in the above formula,

$11 = \frac{89 + x}{9}$

$11*9 = 89 + x$

$99 = 89 + x$

$x = 99 - 89 = 10$

Hence, the ninth number is 10.