This week's puzzle is from the mists of antiquity. There are many variations on the story behind the puzzle, but the puzzle itself remains the same in all of them. We hope you enjoy.
The story goes that a King or other ruler wants to reward one of his subjects and asks what they would like, expecting the request to be for money, gold or something in that vein.
Instead the request is for one grain of rice to be placed a the first square of a chessboard, two grains of rice on the next square, four grains on the next square, and so on, doubling each time.
The King thinks this is a very meagre reward and urges the subject to reconsider, but he is unmoved - this is the reward he wants.
How many grains of rice does he receive?
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Answer at 9.00 on Monday
This is a geometric progression with first term 1 common ratio 2 and number of terms 64.
There is a general formula you can use to sum all numbers in the sequence 1,2,4,8,16,……….etc.It is
1(1-2^64)÷(1-2)
This gives an approximate answer of 1.844674407×10^19