Question

Average lesson g) question​

Answer 1

the answer to the question is 20

Answer 2

$\underline{\textbf{\huge{Question}}}$

Find The AVERAGe of 12 numbers If the average of First 9 numbers is 21 and AVERAGe of last 3 number is 17

$\underline{\textbf{\huge{Answer}}}$



$\boxed{\mathtt{Average=\frac{Sum\:of\:all\:Terms}{Total\:Terms}}}$

In First Case.

AVERAGe of 1st nine Number=21

Let Number and Its Sum=x1+x2+x3 +.....+x9

Total Term=9

So,

$\boxed{\mathtt{\frac{x_1+x_2+x_3+x_4...+x_9}{9}=21}}$

$\boxed{\mathtt{x_1+x_2+x_3+x_4...+x-9=21\times\:9}}$

$\boxed{\mathtt{x_1+x_2+x_3...+x_9=189}}$

MEANS Sum of 1st nine Number=189

Now,

In Second Case Last Three Number

MEANS=x10+x11+x12

Average=17

$\boxed{\mathtt{\frac{x_{10}+x_{11}+x_{12}}{3}=17}}$

$\boxed{\mathtt{x_{10}+x_{11}+x_{12}=17\times\:3}}$

$\boxed{\mathtt{x_{10}+x_{11}+x_{12}=51}}$

Now We get Sum of 1st 9 number=189

And last 3 number Sum=51

Total Sum=189+51=240

Total Number=12

$\boxed{\mathtt{Average=\frac{240}{12}}}$

$\boxed{\mathtt{\huge{Average=20}}}$