The smallest natural number is the unit. If we want to write large numbers we need to look at a larger number of Units. In this way, it is easier to use other number of Units to write bigger numbers. Because of this, we use the Tens which groups the Units into groups of 10.
Thus, we are going to represent 25 Tens as a number. Therefore, this number is:
250
Let's say that the unit we are talking about represents a cube. So, we have 25 groups of ten cubes each, represented as the number 250.