On a see-saw Mary, weight 600N balances John, weight 200N when she sits 1.5m away from the pivot. How far from the pivot is John?

Using the knowledge that the moments are balanced, we can create an equation to calculate the distance John is from the pivot:

600N1.50m = 200N(distance)
(600/200)*1.5 = distance
distance = 4.5m