tiles r/y/g

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advita: Senior | Next Rank: 100 Posts; Posts: 62; Joined: Mon Sep 13, 2010 8:06 pm; Thanked: 2 times

by advita » Tue Jan 25, 2011 10:54 pm

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Source: Beat The GMAT — Data Sufficiency | Tue Jan 25, 2011 10:54 pm

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Tue Jan 25, 2011 11:19 pm

advita 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.

It is much discussed problem which can be answered easily if you note that there is no restriction of what color is coming before green. Before green any one of the three colors may occur. Hence there may be no regularity in the color pattern of the tiles in the row.

As both of the statements individually or together do not provide any relevant information that can establish a regular pattern to the colors of the tiles, the correct answer is E.

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advita: Senior | Next Rank: 100 Posts; Posts: 62; Joined: Mon Sep 13, 2010 8:06 pm; Thanked: 2 times

by advita » Tue Jan 25, 2011 11:44 pm

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.

.....(G)(Y)R.

G (Y)
R (G)

18 19 20 21 22 23 24

(G) Y
(Y) R

thanks anurag...
that means even we cant tell about number 20th also...??

actually i was guessing it is pattern of GYR,GYR,GYR..... so on...

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Tue Jan 25, 2011 11:47 pm

advita wrote:that means even we cant tell about number 20th also...??

actually i was guessing it is pattern of GYR,GYR,GYR..... so on...

No, we can't.
The pattern may be GYR GYR GYR GYR ... or GYR GGG GGG GGG ... or GYR GGG GYR GGG ... etc.

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advita: Senior | Next Rank: 100 Posts; Posts: 62; Joined: Mon Sep 13, 2010 8:06 pm; Thanked: 2 times

by advita » Wed Jan 26, 2011 12:02 am

thanks aurag. it really helpful.

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bala2910: Newbie | Next Rank: 10 Posts; Posts: 1; Joined: Thu Jan 27, 2011 6:34 am

by bala2910 » Thu Jan 27, 2011 6:42 am

Hi Anurag,
I don't understand why GYR-GYR-GYR pattern cannot be allowed. It clearly tells that every yellow tile is preceded by a green tile.
if 18 is G,19 is Y and 20 is R
then 21st must be green and 22nd must be yellow based on the information given. How can 22nd be Green?

18 - 19 - 20 - 21 - 22 - 23 - 24
G Y R G Y R G

21st cannot be Y/R since 20th is R ,therefore 21st is G
22nd Cannot be R/G since 21st is G ,therefore 22nd is Y

My reasoning is that if you say 20 is R, then 22nd can be Y.

Please correct me if I am wrong.

Regards
Bala

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Thu Jan 27, 2011 7:08 am

bala2910 wrote:Hi Anurag,
I don't understand why GYR-GYR-GYR pattern cannot be allowed. It clearly tells that every yellow tile is preceded by a green tile.

No one has ever said that GYR-GYR-GYR ... pattern cannot be allowed.
This is a possible pattern, but not the only one. There can be other patterns too. Just read my earlier posts.

That's because the problem clearly doesn't tells what should precede each green tile. Hence, the tile before any green one may be of any of the three colors.

if 18 is G,19 is Y and 20 is R
then 21st must be green and 22nd must be yellow based on the information given. How can 22nd be Green?

There is no constraints about what comes after a green.
Yellow always preceded by green doesn't mean that green is always followed by yellow.

Hope that clears your confusion.

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