Q:

What does this graph tell about the time complexity?

--X------Y--
0.035   1000
0.089   2000
0.183   3000
0.315   4000
0.502   5000
0.693   6000
0.925   7000
1.222   8000
1.630   9000
1.998   10000
2.234   11000
2.651   12000
3.096   13000
3.667   14000
4.328   15000
4.865   16000
5.496   17000
6.288   18000
7.037   19000
8.036   20000
19.032  30000
34.167  40000
54.505  50000  
Y here corresponds to the no. of random elements taken as input and X is calculated using the function of time in C++ (time.h)  
I wish to know , what can you possibly deduce from this graph about the time complexity of my sorting algorithm?
This graph has time(in seconds) on X-Axis and no. of elements on Y-Axix : http://tinypic.com/r/24cz600/8 Please click on the url

A:

Your Big O is almost certainly n^2.  Time should be on the Y axis, as it is a function of n operations. 

As you can see in the graph, there is a well defined, almost perfect fit to n^2.

