Green and red marbles [2011.II.7]
Source:
March 31, 2011
AMC
Problem Statement
Ed has five identical green marbles and a large supply of identical red marbles. He arranges the green marbles and some of the red marbles in a row and finds that the number of marbles whose right hand neighbor is the same color as themselves equals the number of marbles whose right hand neighbor is the other color. An example of such an arrangement is GGRRRGGRG. Let be the maximum number of red marbles for which Ed can make such an arrangement, and let be the number of ways in which Ed can arrange the marbles to satisfy the requirement. Find the remainder when is divided by 1000.