unisol puzzlesKey90

The challenging logic puzzle for enthusiasts everywhere
logic puzzle

About KEY90  unisol The puzzle-smith  lawrence gould Buy ebook  number puzzle Download ebook  maths puzzle Printed book  key 90 puzzle Puzzle forum  wikipedia entry Logic puzzles 

Key90 is a logic puzzle invented by Lawrence Gould that has been printed in the Sydney Morning Herald (Sydney, Australia) and Tele Sept Jeux (Paris, France) since the mid 1980s.

The puzzle appears in the Sydney Morning Herald as "Unisol" on Mondays, Wednesdays and Fridays. The puzzle is also available in a collected form as an ebook.

Puzzle rules

The rules of the puzzle are:

  1. the letters A to H and J represent the numbers 1 to 9
  2. each letter may occur only once in a row or column
  3. seven letters occur twice; two occur only once
  4. one of the letters that occurs twice has been replaced with an X
  5. the sums of each row and column and the whole square are given
  6. the object is to fill in the numbers.
  7. Each puzzle has a unique solution. One of the numbers that occurs twice and one that occurs once are given, though the puzzles are often more interesting to solve without them.

Solving Key90

Things to look for:

  1. the numbers 1 to 9 add to 45, so the sum of eight letters will give you the value of the ninth
  2. since seven letters occur twice and two only once the puzzle sums to 90 (2* 1 to 9) minus the sum of the two numbers that occur once
  3. certain sums can only be made up of certain numbers e.g. a row that adds to 11 must be 1,2,3 & 5
  4. lines with three letters in common give you the difference between the two other letters
  5. looking at differences between pairs of letters can give the difference between letters or narrow down possible combinations
  6. try to find areas where you can combine pieces of information to reduce possibilities.

Buy the collection - Volume 1

Inside each collection:
- 100 new puzzles - one per page with plenty of room to make notes
- full instructions and helpful hints to get you started
- and the answers

There are several options for buying this collection of unique puzzles:

  • buy and download the electronic PDF book immediately
  • order the ebook by email
  • order a printed book by post

unisol puzzlesKEY90: the unique puzzle with one solution
logic puzzle

About KEY90  unisol The puzzle-smith  lawrence gould Buy ebook  number puzzle Download ebook  maths puzzle Printed book  key 90 puzzle Puzzle forum  wikipedia entry Logic puzzles 

"You solve the puzzle with reasoning, logic and simple arithmetic. It's fun, challenging and addictive."

© 1982 to 2007 Lawrence Gould puzle teaser Mail: PO Box 61, Mt Victoria NSW 2786 Australia
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