A 10-m long plank (of negligible mass) is supported at each end by vertical cables, also of negligible mass. A person of unknown weight sits on the plank between the cables, we do not know exactly where. The tension in the left cable is 300 N, and in the right cable it is 200 N. The person's weight, in N, is?

A 10-m long plank (of negligible mass) is supported at each end by vertical cables, also of negligible mass. A person of unknown weight sits on the plank between the cables, we do not know exactly where. The tension in the left cable is 300 N, and in the right cable it is 200 N. The person's weight, in N, is?