Try to analyze it's graph.

Check the graph on this link:

http://library.thinkquest.org/20991/alg2/graphs.html

now, u'll get to know that [x] is 1 for (1,2) and 2 for (2,2.5).

so, u'll get :

1.dx for (1,2) = 1

and 2.dx for (2,2.5) =1.

So, ans is 2.

Do ask again if any doubt is there.