You are not logged in.

 Discussion: All Topics Topic: Coin Problem Related Item: http://mathforum.org/mathtools/tool/405/

 Post a new topic to the tool: Coin Problem discussion

 Subject: Coin Problem Author: jon Date: Mar 3 2004
http://matti.usu.edu/nlvm/nav/frames_asid_139_g_3_t_2.html

I thought this was a pretty fun applet.  It'd be a great way to start off a
class.  It's a nice brain teaser and gets kids thinking of relationships and
algorithms.

The 9 and 12 and challenge selections were harder than the 8 coin problem.  The
8 coin was very nice in that it told you that the coin was lighter.  This worked
well with my strategy in splitting up the coins in two equal piles and isolating
the one that was lighter than the other one.  I basically kept halving until I
got the counterfeit one.  However with the 9 and 12 case I had to guess and
check starting from the beginning two piles(I would use 4 and 4 with the 9 and
if both were equal then I would know which one was the counterfeit).  My
strategy didn't work well with these other two cases.

Is there an algorithmic method that will eliminate the guessing since we don't
know whether the counterfeit is heavier or lighter? ... and in 2 and 4
weighings, respectively?

I had one technical problem with the appplet.  When I tried taking coins off,
sometimes I would move them off, but they wouldn't really be "off".  The program
would just read it as being on the other side.  Then when I went to weigh again,
the coins that I thought were off would move with that side of the scale.
Perhaps it would be more functional if you had a separate storage space, maybe
use the right 1/3 of the screen for that?  Otherwise, just be careful and don't
rush ... beacause you can't take back weighings you didn't intend on
weighing.

-jon