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Puzzle of the Day

These puzzles are also printed in Eight days a week, a booklet published by the Association of Teachers of Mathematics.The Association of Teachers of Mathematics

Start with a 2 digit number and multiply its digits together then multiply the digits of the new number together and continue until you get a single digit. For instance start with 39, do 3 times 9 to get 27, 2 times 7 gives 14 and 1 times 4 is 4. So 39 gives a chain of 4 numbers. Which start number has the longest chain?

Answer: 77 has 5 numbers in it.


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