There are 4 wrenches just unpacked from a box. They all look the same. There might be one defective item which is either heavier or lighter. Fortunately there is a fifth one that is standard. If you can use a scale to weigh only 2 times, can you find out:
 Is there a defective wrench?
 If there is a defective item, is it heavier or lighter?
It seems like on almost every problem we have people thinking of a scale as the modern day scale that gives us a weight reading. For these problems we are to mean scale as a balance in which you have to compare one side as heavier or lighter. Am I right? (Actually that last question is rhetorical as in the description of the problem type Weights and Scales it says a balanced scale.)
Edited on April 6, 2005, 5:22 pm

Posted by john
on 20050406 17:20:38 