The perimeter of the square is greater than 26 cm, but less than 30 cm. Find the length of the square.

This task can be classified as logical. Indeed, at first glance, it seems that the perimeter of the square can be any number greater than 26, but less than 30, that is, any number from the series: 27, 28, 29. However, in the problem you need to find one value of the perimeter.
Recall that all sides of a square are equal, so its perimeter is equal to the side multiplied by 4. Hence, the perimeter of the square is necessarily divisible by 4 (in fact, this condition is fulfilled only when the length of the side of the square is an integer). Of these options, only 28 is divisible by 4, so the side length of the square is 7.