The perimeter of a square is numerically equal to its area. What is the side length of the square?

S = a * a = a ^ 2, a is the length of the side of the square;

P = a + a + a + a = 4a, a is the side of the square;

S = P;

a ^ 2 = 4a;

a = 4.

Answer: 4.

Explanation: Knowing that the perimeter and area are equal, we equate the area, expressed in terms of the side of the square, to the perimeter, expressed in terms of the side of the square. Divide both sides by a, since a is not equal to 0. We get the answer.