arashyazdiha wrote:In a single row of yellow, green and red colored tiles, every red tile is preceded immediately by a yellow tile and every yellow tile is preceded immediately by a green tile. What color is the 24th tile in the row?

(1) The 18th tile in the row is not yellow.

(2) The 19th tile in the row is not green.

Ans is C!

because until we have a fixed position for a tile, we can't predict 24th tile's color to exact!

Lets take statement 2, it says 19th tile is not green ..-> can be Red or Yellow
but now look at statement 1, it says 18th tile is not yellow..-> can be Red or Green

1,2,3.....18,19,20,21,22,23,24...
if you consider, 19th tile as Red... then 18th tile must be Yellow but according to given Statement 1 it can't be! hence 19th tile must be Yellow!...that's how we can't fix the position of tiles.

arashyazdiha wrote:In a single row of yellow, green and red colored tiles, every red tile is preceded immediately by a yellow tile and every yellow tile is preceded immediately by a green tile. What color is the 24th tile in the row?

(1) The 18th tile in the row is not yellow.

(2) The 19th tile in the row is not green.

The answer is C.

From the question stem you get the ordering of the tiles as G(green)Y(Yellow)R(Red).

Statement 1:
Gives information only about 18 tile, we are not sure whether the 18th tile is red or green.
Insufficient.

Statement 2:
Gives information only about 19th tile, we are not sure whether the 19th tile is red or yellow.
Insufficient.

Combining statements 1 and 2:
The 18th tile is not yellow.
Consider it to be red:
Then the 19th tile should be green.(AS we have the ordering of the tiles as GYR)
But the 19th tile is not green.

So, the 18th tile should be green.

Therefore, the 24th tile is also green, as the ordering repeats after every three tiles(GYRGYRGYR)

Combining 1 and 2.

18th tile can be R or G and 19th tile can be Y or R. But we can't be sure of the color of other tiles as it's not necessary that the tiles always follow GYR pattern. For example we can also have GGGGYR or GYRYGYRGGGGGG etc. This is because G color tile has no restriction.

... R(18th) R(19th) - not possible as R should be preceded by Y.
... R(18th) Y(19th) - not possible as Y should be preceded by G.
... G(18th) R(19th) - not possible as R should be preceded by Y.
... G(18th) Y(19th) - possible but we don't know the pattern of tiles before 18th and after 19th tile as many patterns are possible. For example following are some of the patterns that are possible.

... G(18th) Y(19th) GGGGG
... G(18th) Y(19th) RGGGG
... G(18th) Y(19th) GYGYR
... G(18th) Y(19th) GYRGY

So unless we know that tiles always follow GYR pattern, answer should be E.

If tiles follow GYR pattern, then both the options should be sufficient.

There is no reason to think that the tiles always follow a GYR pattern. They could just as easily go ggggggggggggggggggggg forever.

Once you recognize that 18/19 must be gy, the quickest examples in my view that show that the answer is E are
gyggggg
gyggggy

Keep things simple whenever possible. Using a bunch of g in a row is faster than trying to alternate.

Hi,

GMATBoost u r right, the given data says that every red tile is preceded immediately by a yellow tile and every yellow tile is preceded immediately by a green tile, but it does not say that every green is preceded by some color. So we cannot judge that it follows a particular pattern YRG. As GmatBoos say YRGGGGGGG could happen or YRGY or anything else could happen

So c cannot be the answer.

Answer is E

gmatboost wrote:There is no reason to think that the tiles always follow a GYR pattern. They could just as easily go ggggggggggggggggggggg forever.

Once you recognize that 18/19 must be gy, the quickest examples in my view that show that the answer is E are
gyggggg
gyggggy

Keep things simple whenever possible. Using a bunch of g in a row is faster than trying to alternate.

I thought its C but yes you are right......It should be E in that case, thank you for the explanation...

E