Each side of the square was reduced by 10%. How has its perimeter changed?

Let us denote by the variable x the side of the original square.

Therefore, according to the condition of the problem, we can represent the reduced side of the square in the form: x – x * 10/100 = 0.9x.

Let’s define the perimeter of the original square:

4 * x = 4x.

Let’s define the perimeter of the original square with a reduced side:

4 * 0.9x = 3.6x.

Let’s define how the perimeter has changed:

4x – 3.6x = 0.4x

1 – 3.6x: 4x = 1 – 0.9. = 0.1.

Answer: The perimeter of the square will also decrease by 10%, or by 0.4 of the original side.