TEASER #1:
There are 2 pieces of string. Each piece is made of a different material and of different lengths. Both pieces of string take exactly 1 hour to burn from one end to the other end. The speed of burning is not uniform throughout, so it can burn quickly first, then slowly at the end or in any random way.If you are given only these 2 pieces of strings and a box of matches, how do you measure 45 minutes?
The solution only requires you to burn the strings. No other actions like cutting, measuring, etc., are involved.
This problem was set by a Professor for a Ph.D qualifying exam at Stanford University. Expected to answer in 15 mins.
TEASER #2:
You’re on an island that has no beaches and the sea is full of sharks. The island is 950 metres long and 30 metres wide. A fire starts at one end of the island and there’s a fierce wind blowing towards you. All the grass and trees are very dry and burning rapidly. There are no rocks or sand on the island. There is no boat to make a getaway.
What can you do to save your life?
TEASER #3:
There are ten stacks of ten silver dollars. You are given the weight of a real silver dollar, and are told each counterfeit coin weighs one gramme more than a real silver dollar. You also know that one of the stacks is counterfeit, and you can use a scale that weighs by grammes.
What is the minimum number of weighings needed to determine the counterfeit stack?
[To be continued in the Next Post. Excerpted from the 'Braintertainment' segment of 'Unleashing Genius with the World's Most Powerful Learning Systems' by Dilip Mukerjea. All the images in this post are the intellectual property of Dilip Mukerjea.]
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