This is an interesting question this kind of question was already asked in india's compitative exam UPSC(IAS/IPS) in year 2013. And only toper of this exam can 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)+(13-7)+(7-1)+(9-1)+(13-9)=30

If you solve inside the brackets, you will get the following equation 6 + 6 + 6 + 8 + 4 and by adding all these numbers you will get 30.

or
(7-1)+(15-9)+(11-5)+(13-3)+(3-1) = 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...