Question

Mean weight of m boys is 43 kg. If the teacher who weighs 63kg is included the mean becomes 45 kg.What is the value of m?
(a) 6 (b) 7
(c) 8 (d) 9

Answer 1

(d)- 9


try with options randomly

Answer 2

Answer: Number of boys (m) = 9

Given:

Mean weight of m boys = 43 kg

Weight of teacher = 63 kg

New mean weight = 45 kg

Solution:

$Average\quad weight\quad =\quad \frac { Total\quad weight }{ Number\quad of\quad boys }$

$43\quad =\quad \frac { Total\quad weight }{ m } \quad \longrightarrow \left( 1 \right)$

New average,

$45\quad =\quad \frac { x\quad +\quad 63 }{ m\quad +\quad 1 } \quad \longrightarrow \left( 2 \right)$

On rearranging equation (1), we get

x = 43m

On substituting value of x in equation 2, we get,

$45\quad =\quad \frac { 43m\quad +\quad 63 }{ m\quad +\quad 1 }$

$45m\quad +\quad 45\quad =\quad 43m\quad +\quad 63$

$45m\quad -\quad 43m\quad =\quad 63\quad -\quad 45$

$2m\quad =\quad 18$

$m\quad =\quad \frac { 18 }{ 2 }$

$m\quad =\quad 9$

The mean weight of 9 boys is 43 kg.