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Radioactive Coins (Posted on 2006-10-17) Difficulty: 5 of 5
You have N coins, 2 of which are radioactive. You have a radioactivity detector which can test any subset of the coins at a time, and return the number of radioactive coins in the group (i.e. it returns 0, 1 or 2). You have to find the radioactive coins, using not more than 10 tests. What is the largest N for which this is possible?

No Solution Yet Submitted by David Shin    
Rating: 4.5000 (6 votes)

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Some Thoughts thoughts | Comment 1 of 18
if worst case is taken , answer has to be 64 ....

say 64 = 32+32
2 tests ach give 1 , 1                    ==2

then 16 from 1st and 16 from 2nd ==2

then 8 from 1st and 8 from 2nd     ==2

then 4 from 1st and 4 from 2nd     ==2

then 2 from 1st and 2 from 2nd     ==2

umm i ll think if better way r possible ....

till then my answer is 64

  Posted by siddhesh on 2006-10-17 14:47:51
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