I'm facing with a simple probability problem.

I have a even symmetry function p[k],

p[k] = 0 if |k| > K. p[k] can be any finite even symmetry function.

And I have the same length of random noise n[k].

n[k] follows normal distribution with a variance \sigma^2.

Now I want to find a distribution of following;

<br />
t = \frac{\sum k \cdot d[k]}{\sum d[k]}\\<br />

where  d[k]=p[k]+n[k] . After MATLAB simulation, I realize that t follows a normal distribution. But I cannot derive it.
Would you please give me a hint to solve this problem?

Thanks in advance.