Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?

The horse jumps over the king.
Strangely there is absolutely no scratch on him.

Can anyone explain, how is this possible?

The average age of 10 members of a committee is the same as it was 4 years ago, because an old member has been replaced by a young member. Find how much younger is the new member ?

If you drop a 15 kg iron bar and a 5 kg bag of cotton from a height of 50 meters which will reach the ground first?

In the addition below, all digits have been replaced by letters. Equal letters represent equal digits and different letters represent different digits.
ABCABA
BBDCAA
ABEABB
ABDBAA
------- +
AAFGBDH
What does the complete addition look like in digits?

No matter how little or how much you use me, you change me every month. What am I?

The answer I give is yes, but what I mean is no. What was the question?

What is both possible and impossible at the same time?

I am soft and cuddly that soothe your heart. But, If you pick my last name I am going to tear you all apart. Who am I?