The percentage increase in the area of a rectangle, if each of its sides is increased by 20% is:

To find the percentage increase in the area of a rectangle when each of its sides is increased by 20%, we can follow these steps:

1. Let's assume the length of the rectangle is L and the width is W.
2. The original area of the rectangle is given by A = L * W.
3. If each side is increased by 20%, the new length would be L + 0.2L = 1.2L, and the new width would be W + 0.2W = 1.2W.
4. The new area of the rectangle is given by A' = (1.2L) * (1.2W) = 1.44LW.
5. The percentage increase in the area can be calculated using the formula: (A' - A) / A * 100.
6. Substituting the values, we get ((1.44LW - LW) / LW) * 100.
7. Simplifying further, we have (0.44LW / LW) * 100 = 44%.
8. Therefore, the percentage increase in the area of the rectangle is 44%.

So, when each side of a rectangle is increased by 20%, the area increases by 44%.