Question

Mary wants to decorate her Christmas tree. She wants to place the tree on a wooden block
covered with coloured paper with picture of Santa Claus on it. She must know the exact
quantity of paper to buy for this purpose. If the box has length, breadth and height as 80
cm, 40 cm and 20 cm respectively. How many square sheets of paper of side 40 cm would
she require?

Answer 1

Given that mary wants to paste the paper on the outer surface of the box; The quantity of
the paper required would be equal to the surface area of the box which is of the shape of
cuboid. The dimension of the box are
Length (l)=80cm Breath (b) = 40 cm and height (h) 20cm 
The surface area of thee box = 2[lb+bh+hl]

${\displaystyle =2[80\left(40\right)+40\left(20\right)+20\left(80\right)]}$

${\displaystyle 2\left(5600\right)=11,200c{m}^2}$

The area of the each sheet of paper${\displaystyle =40\times 40c{m}^2}$

${\displaystyle =1600c{m}^2}$

∴Number of sheets required =

${\displaystyle \frac{\text{surface areaa of box}}{\text{area of one sheet of paper}}}$

${\displaystyle =\frac{11,200}{1600}=7}$