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Mathematical Puzzles 



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Puzzle 13 



What 5-digit number am I thinking of?
It has two prime digits. Digit 3 is the highest digit. Digit 2 is the lowest digit. Digit 1 is higher than the sum of digits 4 and 5. Digit 5 is half of digit 4. Digit 1 is one smaller than digit 3. Digit 5 is between digit 2 and digit 1
The digit 0 doesn't appear, and there are no duplicates. Don't forget that 1 isn't prime, but 2, 3, 5 and 7 are prime.

Puzzle Copyright © Kevin Stone

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Puzzle 14 



Last week I drove from Aardvark to Beeville.

On the first day, I travelled 1/3 of the starting distance.

On day two, I travelled 1/2 of the remaining distance.

On day three, I travelled 2/3 of the remaining distance.

At the end of day four, after travelling 3/4 of the remaining distance, I was still 5 miles away from Beeville.

How many miles had I travelled so far?

Puzzle Copyright © Kevin Stone

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Puzzle 15 



Imagine a chessboard of size 20 x 20 instead of the normal 8 x 8.

How many squares, of any size, are there in total?

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Puzzle 16 



My local library decided to hand out some of its old books to the 1,400 people who lived in the town.

To each library member, they offered 6 books, and to each non-member, they offered 4 books.

If only half of the members, and three-quarters of the non-members, accepted the books, how many books were given away?

Puzzle Copyright © Kevin Stone

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