|Spoiler Inside: Solution to Puzzle||SelectShow>|
Fiona has one blue and one green marble. We do not know which is where yet.
Len has a red marble in his right hand.
Nancy has a blue or red marble (i.e. not green) in her right hand.
Len has a blue or green marble in his left hand. (Red is not allowed.)
Nancy must be holding a red marble in her right hand. (The second red marble can not be held by Fiona, and the other two places are next to the first red marble.)
Suppose it is blue. Then Fiona’s marbles are left: blue and right: green (to avoid a pair). The marble in Nancy’s left hand is then green. This gives the order blue-green-blue-red-green-red, but this violates the last condition. This is not a solution.
Suppose it is green. Then Fiona’s marbles are left: green and right: blue (to avoid a pair). The marble in Nancy’s left hand is then green. This gives the order green-blue-green-red-blue-red. This is a solution. There being no other possibilities to try, this is the only solution.