If you see the the figures outside the circle as positive and the figures inside the circle as negative, the bottom row is the sum of the two rows above. For the left column, 3 figures outside the circle + 2 figures outside the circle = 3 + 2 is 5 figures outside the circle. For the middle column, 4 figures inside the circle + 1 figure outside the circle = -4 + 1 = 3 figures inside the circle. The right column = -1 + 3 is 2 figures outside the circle.