Question

A rectangular room is 4.5m long,4m wide and 3m high. Find the cost of white washing it's wall and the roof at rupees 7.50 per sq.m.

Answer 1

area of four walls of a room=2h(l+b)
                                               =2*3(4.5+4) 
                                               =6*8.5
                                               =51sq.m.
area of roof=l*b
                    =4.5*4
                    =18sq.m.
total area=51+18
                 =69sq.m.
cost of whitewashing is rupees 7.50 per sq.m.
hence thecost of whitewashing 69 sq.m.=69*7.5
                                                               =Rs 517.5 

Answer 2

Cost of white washing the wall-
hence the wall is a rectangle so, l×b
=4.5×3
=13.5m sq.
So, cost of white......=13×7.50
=₹975.0
now cost of washing four walls=975×4=₹3900
Now cost of area of the roof=4.5×4
=18.0m sq.
Now, cost of white.... roof= 18×7.50=₹1350.0
Now total cost of white washing the room
=3900+1350
=₹5250