Guess the Weight of the Jug of Water

Using a 2x4 piece of wood we set up a 1st class lever (like a seesaw) and we were given the demonstration with a 5 lb weight and a 20 lb weight. Mr. Olson showed us how to calculate the unknown distance or weight of a force .
Using the equation:
           (mass of object 1)x(distance from fulcrum) + (mass of object 2)x(distance from fulcrum)= 0
Then you solve for the unknown. In this case we had a 5 lb weight and a jug of water with an unknown weight. Our group centered the wood and placed the 5 lb weight 46 inches away from the fulcrum. Moving the jug of water closer and further from the fulcrum we balanced the force of the weights on both sides. The unknown weight was measured to be 26 inches away from the fulcrum.

Solving for the unknown:
            (5lb)x(46in) + (?lb)x(26in)= 0
            230= (?lb)x(26in)
           (230/26)= (?lb)
           ?= 8.85 lbs
After all the groups finished making their guesses we wrote our estimated weights on the white board. Mr. Olson's guess was taking the average of all the group scores which gave us almost the exact weight of 8.7 lbs.

Then we calculated percent error:

[(approximate-exact)/exact] x 100= % error
[(8.85-8.7)/8.7]x 100=?
[.15/8.7]x 100= 1.7% error