This is an interesting question which is asked in india's compitative exam UPSC(IAS) in year 2013. And only Gaurav Agarwal (IAS Topper) could solve it.

The following are the numbers that you can use to fill in the brackets: 1, 3, 5, 7, 9, 11, 13 and 15. You can repeat the numbers if required. The resulting sum should be 30.

(15-9) + (13-3) + (15-1) = 30

If you solve inside the brackets, you will get the following equation 6 + 10 + 14 and by adding all these numbers you will get 30.

This is not mention in above question that you can use sign or not. Thus we can use the sign (+, -, x etc ).
Because in the given question it is also mention that we can repeated the numbers. So wee can also solve it as...