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DS -1

by sparsh.21 » Sat Jan 03, 2009 10:55 am
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.


OA E
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Source: — Data Sufficiency |
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Re: DS -1

by Stuart@KaplanGMAT » Sat Jan 03, 2009 12:46 pm
sparsh.21 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.
We need to make sure we're not making any assumptions about what we don't know. For example, just because every yellow tile is preceded by a green tile, that doesn't mean every green tile is followed by a yellow tile.

(1) 18th is not yellow.

Well, 18-24 could all be green.
18 could be green, and 19-24 could be YGYRGY, so 24 could be yellow. Insufficient.

(2) 19th is not green.

Well, 20-24 could all be green.
19 could be red, and 20-24 could be GYRGY, so 24 could be yellow.
Insufficient.

Together:

24 could still be either yellow or green: insufficient, choose(E).
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by sparsh.21 » Sat Jan 03, 2009 10:08 pm
Thanks Stuart
I made the same bad assumption there ...!!!
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by mental » Sun Jan 04, 2009 12:20 am
Thanks Stuart.
I made the same assumption which you pointed out as false :(
and then went into thinking why anymore info is required.
The question itself says 24th tile is Red!!!
Both statements are irrelevant

And then :?: why the choices then
couldnt get Head or tail of choices, opted E (LUCKY) :)
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by rajataga » Sun Jan 04, 2009 3:36 am
i solved this in a slightly different way...

the color preceding red and yellow is given, however the color preceding green is not given, hence green is not given....

so after any color there could be 2 different colors following, red or yellow (depending on the previous tile), and green, except in the case of red, which can only be succeeded by green....

so the only case in which we could determine the color of the 24th tile would be if the 23rd tile was given to us as red.....in all other cases we CANNOT narrow down the answer to 1.

Hence, E...
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