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Wrenches (Posted on 2004-07-02) Difficulty: 2 of 5
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:
  1. Is there a defective wrench?

  2. If there is a defective item, is it heavier or lighter?

  Submitted by Brian Smith    
Rating: 2.8333 (6 votes)
Solution: (Hide)
Call the standard wrench S and the four other wrenched A, B, C, and D.

Weigh AB vs CS

Case 1: AB equals CS
Weigh S vs D: If S equals D then none are defective. If S is heavier than D then D is defective and light. If S is lighter than D then D is defective and heavy.

Case 2: AB is heavier than CS
Weigh A vs B: If A is heavier than B then A is defective and heavy, If A is lighter than B then B is defective and heavy, If A equals B then C is defective and light.

Case 3 AB is lighter than CS
Weigh A vs B: If A is heavier than B then B is defective and light, If A is lighter than B then A is defective and light, If A equals B then C is defective and heavy.

Comments: ( You must be logged in to post comments.)
  Subject Author Date
Scale or balancejohn2005-04-06 17:20:38
Cool QuestionLozza2004-09-13 04:06:32
Here is solution...Patricia Stamets2004-07-04 22:59:23
re: SolutionShadow2004-07-04 16:41:36
Some Thoughtsre: A shotAdy TZIDON2004-07-03 02:13:26
SolutionA shotrohit2004-07-03 00:30:20
re(3): Balanced solutionArunava Dutta2004-07-02 11:00:30
re(2): Balanced solutionEric2004-07-02 10:52:04
re(2): Balanced solutionfwaff2004-07-02 10:33:39
Some Thoughtsre: Balanced solutionArunava Dutta2004-07-02 10:31:49
SolutionBalanced solutionfwaff2004-07-02 10:26:09
Solutionre: Solution - My solutionArunava Dutta2004-07-02 10:23:33
Some ThoughtsSolutionEric2004-07-02 09:17:57
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