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In a single row of yellow, green and red colored tiles [#permalink]
01 Mar 2013, 10:20

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Difficulty:

55% (hard)

Question Stats:

44% (02:13) correct
56% (01:34) wrong based on 95 sessions

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?

Re: In a single row of yellow, green and red colored tiles [#permalink]
01 Mar 2013, 10:29

We don't know what precedes green tiles. It could be anything, which means that green can follow tiles of any color.

Also, it's worth mentioning that green can be followed by any color tile, not only yellow, because the rule about yellow tiles being preceded by green tiles doesn't preclude the possibility of other tiles also being preceded by green tiles.

In short, we could have a whole string of green tiles between the 18th and 24th tiles.

Re: In a single row of yellow, green and red colored tiles [#permalink]
09 Mar 2013, 10:02

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Consider stmt 1: 18th tile is not yellow. Therefore, it should be green/red (given: there are only 3 colors). If we have green color on 18th tile, then the order is: 18th - green (G) 19th - yellow (Y) 20th - red (R) 21th - G 22nd - Y 23rd - R 24th - G Ans: Green Similarly, if we consider 18th tile to be of red color, then we get 24th tile to be of red color. Hence Stmt 1 is not sufficient Now, consider Stmt 2. 19th tile should be Y/R color. If we take Y, then 24th tile is G and if we take R, then 24th tile is Y. Hence, stmt 2 is not sufficient. If we consider both stmts together, then 18th tile should be G and 19th should be Y which gives the answer as G. Therefore, neither of the stmts alone is sufficient but both when used together are sufficient.

Re: In a single row of yellow, green and red colored tiles [#permalink]
14 Mar 2013, 02:43

revanthnov wrote:

Consider stmt 1: 18th tile is not yellow. Therefore, it should be green/red (given: there are only 3 colors). If we have green color on 18th tile, then the order is: 18th - green (G) 19th - yellow (Y) 20th - red (R) 21th - G 22nd - Y 23rd - R 24th - G Ans: Green Similarly, if we consider 18th tile to be of red color, then we get 24th tile to be of red color. Hence Stmt 1 is not sufficient Now, consider Stmt 2. 19th tile should be Y/R color. If we take Y, then 24th tile is G and if we take R, then 24th tile is Y. Hence, stmt 2 is not sufficient. If we consider both stmts together, then 18th tile should be G and 19th should be Y which gives the answer as G. Therefore, neither of the stmts alone is sufficient but both when used together are sufficient.

If we consider both statement togather, then according to st-1 - 18th tile could be Red or Green. Not clear and as per st-2, 19th tile could be Red or Yellow.

18th tile - R or G 19th tile - R or Y 20th tile - can not decide, SO E

Re: In a single row of yellow, green and red colored tiles [#permalink]
14 Mar 2013, 20:37

Expert's post

mun23 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.

In questions such as these, some structured reasoning helps out. Write down little tit-bits of information to get a clear picture and avoid confusion.

Say, if see a Red tile, I will see YR together. Similarly, if I see a Yellow, I will see GY together. Updating - if I see Red, I will see GYR

So take a moment to think what the row could look like before jumping on to the statements:

GGGGGGGGGGGGGGGGGGGGGGGGYR or GYGYGYGGYGYGGGGGGGGGYRGGGG or GYRGGGGGYGGGGGYGGGGGGGYRGGG etc

That is, there are no constraints on G. Before a Y, I will see a G and Before an R, I will see GY.

Now look at the statements:

(1) The 18th tile in the row is not yellow. So 18th tile is G or R. There are no constraints on what will come AFTER G or R so we cannot decide the color of 24th tile. 18th to 24th tiles could look like this: GGGGGGG or GYGYGYR etc

(2) The 19th tile in the row is not green. So 19th tile is Y or R. Again, there are no constraints on what will come AFTER Y or R so we cannot decide the color of 24th tile. 18th to 24th tiles could look like this: GYGGGGG or GYGYGYR etc

Taking both together, if 19th tile is R, 18th tile must be Y but it cannot be according to statement 1 so 19th tile must be Y and 18th tile must be G. But still, do we have any constraints on the 24th tile? We can have any tile after the 19th Y tile - R or G. 18th to 24th tiles could look like this: GYGGGGG or GYGYGYR etc

Re: In a single row of yellow, green and red colored tiles [#permalink]
19 Jun 2014, 04:26

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