Answer:
Insufficient data.
Step-by-step explanation:
Given,
Green and red coloured tiles, every red tile is preceded immediately by a yellow tile and every yellow tile is preceded immediately by a green tile,
That is,
The order of tiles is,
Red(R), yellow(Y), green(G)
(1) if 18th tile is not yellow,
Then, possible 18th tile = red or green
Order 18 19 20 21 22 23 24
Tile R/G Y/R G/Y R/G Y/R G/Y R/G,
(2) If 19th tile in the row is not green.
Then possible 19th tile = yellow or red,
Hence, the data is incomplete to tell what is the colour of 24th tile.
