Neighbourhood watch
In my street the odd-numbered houses are on the left and the even-numbered houses are on the right. The first house on the left, number 1, is immediately opposite number 2, then number 3 is opposite number 4, and so on. Each house has its number on the gate.
On a recent walk I started at house number 1 and walked up the left-hand side of the road to the very end, then I crossed to the house opposite and walked back down the right-hand side until I reached my own house.
I counted the number of occurrences of the digit 1 that I had seen on the gates, and the number of occurrences of the digit 2: after entering my own gate the product of these two totals was a two-figure number.
Had I stopped counting at the house opposite my own, then the product would have been smaller; in fact it would have been the reverse of the eventual product.
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What is my house number?
WIN £15 will be awarded to the sender of the first correct answer opened on Tuesday 19 August. The Editor’s decision is final. Please send entries to Enigma 1503, Â鶹´«Ã½, Lacon House,84 Theobald’s Road, London WC1X 8NS, or to enigma@newscientist.com (include your postal address).
Answer to 1639 Square clocks: the square is 49; x = 5, 9 and 15
The winner David Croome of Par, Cornwall, UK
