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Finding Good Batteries (Posted on 2013-11-11) Difficulty: 3 of 5
My remote control needs two new batteries, but when I went to get replacements I found that the four good batteries got mixed in with four bad batteries. The only means of determining if the batteries are good is to put two into the remote and see if it works. The remote works with two good batteries and is unresponsive if I have at least one bad battery in it.

What is the minimum number of tries I need to guarantee that I get two good batteries?

See The Solution Submitted by Brian Smith    
Rating: 5.0000 (1 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
Solution my(IMPROVED ) answer and exolanation | Comment 6 of 8 |
Better solution:

a.  Divide the 8 batteries into three sets - 123,456,78. 

b.  Analyze the 1 st set n 1-2 1-3 2-3, if all failed there is at most
one good battery in this set.

c . Same procedure with 456 set.

If this set failed as well , both 7 and 8 qualify.

So, the maximum  # of tests   needed is 6(six).

  Posted by Ady TZIDON on 2013-11-12 02:58:40
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