Expert: Steve Holleran - 5/6/2008

Question
Weights of 2, 3, 5, and 7 pounds are not labeled. Using a balance scale. How many weighting do you need to determine what each weight is?

Please Show Work or explanation

Thank You Very Much For Your Help

Answer
Hi Steve,

I would think you would need 4 weighings.

Pick two, weigh them , keep the heavier and set the lighter aside.

Pick one of the remaining two, balance it with the one from the first try, and keep the heavier.  Since this is heavier than two items, it must be the 5 or the 7.

Weigh it with the remaining one, and the heavier has to be the 7.  The other one is the 5, and then compare the two left over to determine the 2 and 3.

Steve