Question

The length, breadth and height of a room are $5m$, $4m$ and $3m$ respectively. Find the cost of white washing the walls of the room and the ceiling at the rate of $Rs.7.50per{m}^2$

Answer 1

Given, length of the room, $l=5m$

Breadth of the room, $b=4m$

Height of the room, $h=3m$

Area of the ceiling, $A_1=l\times b$

$=5\times 4m^2$

$=20m^2$

Area of the $2$ walls, $A_2=2\times l\times h$

$=2\times 5\times 3$

$=30m^2$

Area of the other $2$ walls, $A_3=2\times b\times h$

$=2\times 4\times 3$

$=24m^2$

$\therefore$ Total area of the walls and the ceiling

$=A_1+A_2+A_3$

$=20+30+24$

$=74m^2$

It is given that, the cost of white washing is $Rs.7.50per{m}^2$

Thus, cost of white washing$=$ Rs. $7.50\times 74$

$=$ Rs. $555$

(OR)

Area of four walls room $=2h(l+b)$

$=2\times 3m(5m+4m)$

$=6m\times 9m$

$=54c{m}^2$

Area of the ceiling $==l\times b$

$=5m\times 4m$

$=20m^2$

Now, Area of the four walls and area of ceiling

$=54c{m}^2+20m^2$

$=74m^2$

It is given that, the cost of white washing is $Rs.7.50per{m}^2$.

$\Rightarrow$ cost of white washing $=Rs.7.50\times 74=Rs.555$