Question

_+_+_=30 (fill the answer using 1,3,5,7,9,11,13,15).

Answer 1

This sum can only solve by using factorial
3 factorial means 3x2x1=6
3 factorial+9+15=30

Answer 2

 The concept of factorial is used here.
Factorial is the product of all the numbers from 1 to that number.
Therefore, according to he question, 
4!+5+1=4*3*2*1 + 5+ 1
           = 24+5+1=30
Similarly, you can find many such answers!!