Here's an easy way to sum up all the numbers in a 3 by 3 date block on your calendar. It's not magic ... it's mathematical! Pedagogical side: This segment introduces the notion of the average: the number in the middle of the block is the average of the nine numbers that form the block. By adding all the numbers together and dividing by nine (the number of squares), the answer is the number in the central position. To find the sum of the nine numbers quickly, it is a question of multiplying the number in the center by 9.