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Sunday Times Teaser 2750 – Granny’s Birthday

by Graham Smithers

Published: 7 June 2015 (link)

At Granny’s birthday this year she was telling us some surprising things about some past birthdays. She told us that each year she writes down the date of her birthday (in the eight-digit form dd/mm/yyyy) and her age in years. On two occasions in her lifetime it has turned out that this has involved writing each of the digits 0 to 9 exactly once. The first of these occasions was in 1974.

What is Granny’s date of birth (in the eight-digit form)?

3 Comments Leave one →
  1. Brian Gladman permalink

    • Frits permalink

      I just saw Jim’s version of this Teaser.

      “age_digits” sometimes contains three digits (which should not be allowed).

      example: (y, m, d) = (1986, 3, 22) age_digits = (‘5’, ‘4’, ‘7’)

      You don’t seem to check that 1974 is the first year she could write each of the digits 0 to 9 exactly once (as you check all years after 1974). Maybe there are more solutions before 1974.

      It makes more sense not to store entries in “dm” that don’t pass the “before 7th June” check.

      • Brian Gladman permalink

        Hi Frits,

        The “age_digits” issue won’t occur in my solution above since it checks for different digits.

        If there was a solution with two dates, the first of which is earlier than 1974, the teaser would then be faulty. I hence assumed the author had posed it correctly.

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