Question

A plastic box1.5m long,1.25m wide and65cm deep is to be made. it is opened at the top. ignoring the thickness of the plastic sheet, determine:. (1) the area of the sheet required for making the box. (2). the cost of sheet for it. if a sheet measuring 1m² costs Rs20

Answer 1

area of sheet =2(hl+ bh) + hl
=2( 0.65×1.5+1.25×0.65)+1.5×1.25
=5.45 m^2


now ,
cost = area x rate
= 5.45×20
=109 Rs

Answer 2

length , l = 1.5 m
breadth = 1.25 m
height , h = 65 cm = 0.65 m

1)
As the plastic box is opened at the top , 
Area of sheet required = L.S.A + 1 Base area 
                                     = 2 ( l + b)× h + lb
                                     = [2 × (1.5 + 1.25 ) × 0.65] + [1.5 × 1.25 ] 
                                     = [2 × 2.75 × 0.65] + 1.875
                                     =  3.575 + 1.875
                                     = 5.45 m²

Cost of sheet of 1 m² = Rs 20
Total cost for 5.45 m² of sheet = 5.45 × 20
                                                 = Rs 109