Question

The average of three numbers is 12. If two of these If the numbers are 13 and 15 then what will be the third number?​

Answer 1

               here the average of  three no. are 12

           and two no. are 13 and 15, let the third no. be x

according to question,

                                        13+15+x /3=12

                                        28+x=36

                                         x=36-28

                                          x=8

                       hence the third no. be 8.

Answer 2

$\textbf{\underline{\underline{Answer :-}}}$

$\text{The Third number is 8}$

$\textbf{\underline{\underline{Explanation :-}}}$

$\textsf{\underline{\underline{Given :}}}$

Average of the numbers = 12

The given 2 Numbers = 13 and 15

Total Observations = 3

$\textsf{\underline{\underline{To find : }}}$

The third number

$\textsf{\underline{\underline{Solution :}}}$

Consider the number as x

Average/Mean =

$\tt{\implies \dfrac{sum \: of \: \: observations}{total \: observations} }$

$\tt{\implies \dfrac{x + 13 + 15}{3} = 12 }$

$\tt{\implies \dfrac{x + 28}{3} = 12 }$

$\tt{\implies \: x + 28 = 12 \times 3}$

$\tt{\implies \: x + 28 = 36}$

$\tt{\implies \: x = 36 - 28}$

$\tt{\implies \: x = 8}$

$\large{\boxed{\bigstar{\sf \: {x = 8 }}}}$

$\therefore$$\text{The Third number is 8}$

$\textbf{\underline{\underline{Verification :-}}}$

$\tt{\implies \dfrac{x + 13 + 15}{3} = 12 }$

$\tt{\implies \dfrac{8 + 13 + 15}{3} = 12 }$

$\tt{\implies \dfrac{36}{3} = 12 }$

$\tt{\implies 12 = 12 }$

${\boxed{\bigstar{\sf \: { LHS = RHS }}}}$

$\therefore$$\text{The Third number is 8}$