Three-cornered problem
I have a set of equal-sized equilateral triangles, white on one face and black on the back. On the white side of each triangle I have written a number in each corner. Overall the numbers run from 1 to my age (which is less than thirty). If you picture any such triangle then it occurs exactly once in my set (for example, there is just one triangle containing the numbers 1, 1 and 2; but there are two triangles containing the numbers 1, 2 and 3).
The number of triangles that contain at least one even number is even.
The number of triangles that contain at least one odd number is odd.
The number of triangles that contain at least one multiple of four is a multiple of four.
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How old am I?
Send your solution to: The Sunday Times Teaser 3071, PO Box 29, Colchester, Essex CO2 8GZ or email puzzle.entries@sunday-times.co.uk. The first two correct solutions opened after next Saturday win £20. Open to 18+ UK & ROI residents only.
Solution to Teaser 3069
10
The winners are: B Smith, Brighton; Jim Randell, Builth Wells.