### IMO 1970

**Problem B1**
Find all positive integers n such that the set {n, n+1, n+2, n+3, n+4, n+5} can be partitioned into two subsets so that the product of the numbers in each subset is equal.

**Solution**

The only primes dividing numbers in the set can be 2, 3 or 5, because if any larger prime was a factor, then it would only divide one number in the set and hence only one product. Three of the numbers must be odd. At most one of the odd numbers can be a multiple of 3 and at most one can be a multiple of 5. The other odd number cannot have any prime factors. The only such number is 1, so the set must be {1, 2, 3, 4, 5, 6}, but that does not work because only one of the numbers is a multiple of 5. So there are no such sets.

Solutions are also available in: Samuel L Greitzer, International Mathematical Olympiads 1959-1977, MAA 1978, and in István Reiman, International Mathematical Olympiad 1959-1999, ISBN 189-8855-48-X.

12th IMO 1970

© John Scholes

jscholes@kalva.demon.co.uk

6 Oct 1998

Last updated/corrected 26 Jan 04