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 Divide into Primes (Posted on 2005-09-17)
The coins currently in circulation in Britain are for 1p, 2p, 5p, 10p, 20p, 50p, 100p and 200p. When I gave one of each of these coins to Tom and Harry to share between them, each took two or more coins, with each person's coins' total value equal to a prime number of pence. No coins were left over.

I asked Harry whether his share was a specific number of coins that I mentioned. He said "no".

I then asked Harry whether he had the coin of a denomination I specified. He said "yes".

His two answers allowed me to determine the total of the value that Harry had taken. What was that value?

 See The Solution Submitted by Charlie Rating: 3.2857 (7 votes)

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 re: Coincidence and binary searches | Comment 7 of 12 |
(In reply to Coincidence and binary searches by Steve Herman)

One simple scheme would be to ask Harry if he has a 1p coin, and then if he has a 200p coin, and if he has a 10p coin.  This will always be enough to determine his coins, no matter what his answer.
 Posted by Steve Herman on 2005-09-18 12:52:54

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