Sum of moments in equilibrium must equal 0. The sum of clockwise moments must equal the sum of anticlockwise moments. W1 is the force exerted on the seesaw by the heavy person at distance D1 from the pivot and W2 is the force exerted by the lighter person at distance D2 from the pivot. Moment = perpendicular distance * forceW1 = 2 * W2Therefore, in order for the system to be in equilibrium, W1D1 = W2D2. Rewritten as 2W2D1 = W2D2.W2 cancels out and we are left with the ratio of distances from the people to the pivot point, D1/D2 = 1/2