Question

?+?+?+?+?= 30, use only 1,3,5,7,9,11,13,15 , you can use repeated nos if you can .

Answer 1

(15-9)+(13-7)+(11-5)+(9-3)+(7-1)=6+6++6+6+6=30

Answer 2

Gaurav Agrawal answered very intelligently and using his imagination.         -- really for this question is asked so many times.. all credit goes to him.

you can answer this question in many ways using the factorial function.

3! + 3! + 3! + 3! + 3!      = 30 
   3! + 1 + 3 + 9 + 11          = 30
       1 + 5 + 7 + 3! + 11               = 30
             3! + 3! + 3! + 11 + 1             = 30
                 3! + 3! + 11 + 5 + 1               = 30
            11+ 1 + 1 + 3! + 11              = 30
       15 + 3 + 3 + 3 + 3!              = 30
     13 + 1 + 1 + 9 + 3!            = 30
         13 + 1 + 3 + 7 + 3!            = 30
               13 + 5 + 3 + 3 + 3!            = 30

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You need one operator for which the result is an even number with an input being an odd number.  Factorial is one.  Probably there are other operators too.