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  Driven crazy
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  Pirate treasure
• 
  Use your head
• 
  Which way?
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  All around the world
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  Hats off
• 
  Shed some light
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  Einstein's riddle
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  Figure it out

Puzzles

Hats off!

An island off the English coast has a population of 100. 25 of them always wear green hats and 75 always wear yellow hats. Nobody on the island knows how many green and yellow hats there are altogether, or what colour their own hat is. All they know is that at least one person on the island has a green hat.

Each year, everyone goes to a party in the island's village hall, which is only for people wearing yellow hats. If someone realises they're wearing a green hat, they have to leave at the end of that day and not return the next day. But, due to the islanders' diffidence, nobody mentions it if someone with a green hat turns up. How many days does it take before there are no people with green hats at the party?

Reveal answer