Question

____+____+____+=30 using 1,3,5,7,9,11,13,15

Answer 1

The sum of three odd numbers gives an odd number
So, the sum of 3 given odd numbers doesnt results 30
So, it is an impossible factor
here we can't use 3! too
because 3! [3×2×1] results a even number 6
so we cant use it.

Answer 2

This is not solvable in the normal arithmetic method of addition of the numbers given.  We have to have three even numbers or  one even number and two odd numbers to get the result as an even number.  But we don’t have any odd number in the given set of numbers in the parentheses.

We need to use an operator like  a factorial or some other one, which yields an even number taking an odd number as the input.  Logarithm is an operator or a function which also can give an even number.

It is left to imaginative skill and knowledge of the person to answer this question.

     3!   +  11  + 13    = 30
     3!   + 15 +  9      = 30
 
     15 + 15 + Log 1  = 30          ,  as Log 1 = 0  to any base.
     15 + 15 + Ln 1    = 30        as Ln 1 = 0    to any base
      15 + 13 + Log₃ 9  = 30,    as  Log₃ 9 = 2      ( base 3)
      3*7 + 9 + Log 1  = 30
 
    15  +  13  + 3!/3  = 30          using division operator in between
     (1+3)! + 1 +  5    = 30
     3³  +  3! / 3 +  1    = 30
     9  +  1  + 5! / 3!    = 30
     15³/5³  + 1 + 3! / 3  = 30          using cube and division operators.