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        riddles >> medium >> 8 coins with two heavier coins
        
(Message started by: wonderful on Apr 24^th, 2008, 4:39pm)

Title: 8 coins with two heavier coins
Post by wonderful on Apr 24^th, 2008, 4:39pm

There are 8 coins. The two coins X, and Y are heavier. Using the standard two-arms balance scale determines X, Y by 5 weightings. Also, determine if X>Y, X=Y or X<Y.

Have A Great Day!

Title: Re: 8 coins with two heavier coins
Post by rmsgrey on Apr 25^th, 2008, 3:50am

on 04/24/08 at 16:39:06, wonderful wrote:

There are 8 coins. The two coins X, and Y are heavier. Using the standard two-arms balance scale determines X, Y by 4 weightings. Also, determine if X>Y, X=Y or X<Y.

Have A Great Day!

Assuming you don't already know which coins are X and Y to start with, how can you tell which is X and which is Y when you find the odd pair in order to tell which of the two is the heavier one?

Title: Re: 8 coins with two heavier coins
Post by Grimbal on Apr 25^th, 2008, 7:32am

It could be you need to identify the 2 coins and tell which one is heavier or whether they are both of the same weight.

Now let's see. 2 coins in 8 is 28 possibilities. Times 3 for the 3 relative weights. So you have 84 cases to distinguish.

But 4 3-way measurements can identify at most 81 cases.

Title: Re: 8 coins with two heavier coins
Post by wonderful on Apr 25^th, 2008, 1:15pm

Thanks guys. Grimbal's observation is correct. I have revised the question accordingly.

Have A Great Day!