Question

[ ]+[ ]+[ ]=30By using 1,3,5,7,9,11,13,15Numbers can be repeated

Answer 1

The sum of three odd numbers gives an odd number
So, the sum of 3 given odd numbers doesn’t 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 can’t use it.
If there will be an allowance of factorials, then the answers will be
3! + 15 + 9 =30
3! + 11 + 13 = 30

Answer 2

Hey there!
We have been learning since primary that the sum of any odd numbers taken odd times is never even.
Eg : 1 +7+3+5+7 = 23 
Is 23 even ? Nope! Its not.
Similarly, sum of any odd numbers taken at odd times cannot be even, its always odd.You can't change a maths rule alright, you can't say 1+1 = 5.Is it ? No, its not 

And yeah,for general knowledge, this is one question that has been forwarded in the social media to fool people and yes people are befooled.They are misunderstanding primary maths.
So, better you don't get fooled because I believe you know maths :)


But, if you really want to know maths.
There is a method 
3! + 11 + 13 
= (3×2×1) + 11 + 13
= 6 + 11 + 13
= 30

That's called factorial and you will learn it in higher classes. :)