Question

1,3,5,7,9,11,13,15?
x+x+x=30

Answer 1

i)   3!+1+3+13+7=30              [ If we solve by factorial method]
ii)   3!+3!+3!+3!+3!=30
     [3!=3×2×1=6]

[without factorial method]
Odd nos added for odd nos. of time will always give an ODD NUMBER.
Odd nos added for even no of time will give an EVEN NUMBER.