Each of A, B and C is a positive integer such that:
20*A, 6*B and C are in arithmetic sequence, and:
20*A, 6*B and C+1 are in geometric sequence

Find the six smallest values of A+B+C

(In reply to Possible Solution by Jer)

I found (A,B,C) = (5,15,80) is an answer with progressions 100, 90, 80 or 81.  This corresponds to d=-10.  The sum A+B+C is 120 in this case.

Posted by Brian Smith on 2016-03-24 13:52:42