The question that follows came in the UPSC final exam that was held in December 2013. Only one examinee i.e. Gaurav Agarwal was able to solve it. Can you solve it?

? + ? + ? + ? + ? = 30

You have to fill numbers in place of question marks. The numbers that you can use are 1, 3, 5, 7, 9, 11, 13 and 15. You can repeat the numbers if you like.

The answer is

(15 - 9) + (13 - 7) + (7 - 1) + (9 - 1) + (13 - 9)

If you calculate it, you will get

6 + 6 + 6 + 8 + 4 = 30