Problem:
A painting 40 cm long and 28 cm wide is painted on a cardboard such that there is a margin of 2 cm on each of its sides. Find the total area of the margin.

Solution:

To find the total area of the margin, we need to calculate the area of the cardboard and subtract the area of the painting.

1. Calculating the area of the cardboard:
The cardboard has a length of 40 cm and a width of 28 cm. To find the area of the cardboard, we use the formula:
Area = Length x Width

Let's substitute the given values into the formula:
Area of the cardboard = 40 cm x 28 cm = 1120 cm²

2. Calculating the area of the painting:
The painting is done on the cardboard, leaving a margin of 2 cm on each side. To find the width and length of the painting, we need to subtract twice the margin width from the total width and length of the cardboard.

Width of the painting = Width of the cardboard - 2 x Margin width
Width of the painting = 28 cm - 2 cm - 2 cm = 24 cm

Length of the painting = Length of the cardboard - 2 x Margin width
Length of the painting = 40 cm - 2 cm - 2 cm = 36 cm

Now, we can calculate the area of the painting using the formula:
Area = Length x Width

Substituting the values:
Area of the painting = 36 cm x 24 cm = 864 cm²

3. Calculating the total area of the margin:
To find the total area of the margin, we subtract the area of the painting from the area of the cardboard.

Total area of the margin = Area of the cardboard - Area of the painting
Total area of the margin = 1120 cm² - 864 cm² = 256 cm²

Therefore, the total area of the margin is 256 cm².

2x 68