Recycling points
The recycling plant accepts glass, metal and plastic items. For every four items of the same type that I feed it I receive 1 green point, so I will receive 10 points whether I feed it 40, 41, 42 or 43 plastic items.
I fed it a 2-digit number of glass items, a larger 2-digit number of metal items and an even larger 2-digit number of plastic items. I received a 1-digit number of points for each type of item. The digits 1 to 9 each appeared only once among those 2-digit and 1-digit numbers.
If I told you the total number of items that I fed it you would be able to deduce with certainty how many of them were glass, how many were metal and how many were plastic.
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How many were metal?
WIN £15 will be awarded to the sender of the first correct answer opened on Wednesday 27 May. The Editor’s decision is final. Please send entries to Enigma 1542, Â鶹´«Ã½, Lacon House, 84 Theobald’s Road, London WC1X 8NS, or to enigma@newscientist.com (please include your postal address).
Answer to 1536 List of primes: The sum of the prime numbers is 1287
The winner Bill Payne of Westfield, Surrey, UK