I found two using a little C# program:
9,10,11,12,13,14,15,16
and
18,19,20,21,22
(if you're interested in the program drop me a msg)
the airplane new altitude is 17500
20000-2500=17500
Answer:
There are 26 tiles in the bag.
To spell the word DOT, we have to select 3 tiles from the bag.
This can be done in
26C3 ways.
Out of this, the word DOT can be correctly spelled in only 1 way.
Hence, the Prob.
=1 / 26C3