Hi fourteenstix,

What is the source of this question? I ask because the "intent" of this question might not match the "logic" of this question. The information at the beginning of the prompt is "causal" but only deals with tiles that PRECEDE other tiles; we have to deduce what tiles can FOLLOW other tiles. We know what comes immediately before a red (a yellow) and we know what comes immediately before a yellow (a green), but we're not told what comes before a green.

Up-Front Deductions:
A Green can be followed by another Green or a Yellow (but not a Red)
A Yellow can be followed by a Green or a Red (but not a Yellow)
A Red can be followed by a Green (but not a Yellow or Red)

We're asked for the 24th Tile....

Fact 1: 18th = NOT Yellow, so 18th = Green OR Red

If 18th = Red
we would have G, G, G, G, G to infinity, so the 24th Tile = GREEN

If 18th = Green
we COULD have G, G, G, G, G, Y, so the 24th Tile = YELLOW

Inconsistent = INSUFFICIENT

Fact 2: 19th is NOT Green, so 19th = Yellow OR Red

If 19th = Red
we would have G, G, G, G, G, so the 24th Tile = GREEN

If 19th = Yellow
we could have R, G, G, G, Y so the 24th Tile = YELLOW

Inconsistent = INSUFFICIENT

Combining Facts:

18th = Green OR Red
19th = Yellow OR Red

Since Red can only be followed by GREEN, the 18th Term CAN'T be Red!

So, 18th = Green and
19th = Yellow
we could have G, G, G, G, G, so the 24th = GREEN
we could have G, G, G, G, Y, so the 24th = YELLOW
Inconsistent = INSUFFICIENT

Final AnswerE

GMAT assassins aren't born, they're made,
Rich

Hi fourteenstix,

I absolutely agree; the GMAT is not likely to give you a question that is designed in this way. While you will see some sequence-based questions, those questions tend to be well-defined so that you don't have to spend too much time figuring out how the sequence "works." Like typical sequence questions though, this prompt did require you to figure out the pattern behind the sequence.

GMAT assassins aren't born, they're made,
Rich