Mary wants to decorate her Christmas tree. She wants to place the tree on a wooden block covered with colored paper with a picture of Santa Claus on it.

Solution:

Given that:

Mary wants to paste a paper on the outer surface of the wooden block. The quantity of the paper required would be equal to the surface area of the box which is of the shape of a cuboid.

The dimensions of the wooden block are:

Length (l) = 80 cm

Breadth (b) = 40 cm

Height (h) = 20 cm

Surface Area of the wooden box = 2[lb + bh + hl]

= 2[(80*40) + (40*20) + (20*80)]

= 2[5600]

$=11200 \mathrm{~cm}^{2}$

The Area of each sheet of the paper $=40 \times 40 \mathrm{~cm}^{2}$

$=1600 \mathrm{~cm}^{2}$

Therefore, the number of sheets required $=\frac{\text { Surface area of the box }}{\text { Area of one sheet of paper }}$

=11200/1600

= 7

So, she would require 7 sheets.