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?

Manish has to secure 40% marks to pass his B.tech final exams.
He got just 40 marks and failed by 40-marks.

What is the maximum marks?

How many times can you subtract the number two from the number fifty?

I am white when I am dirty, and black when I am clean. What am I?

It comprises roots which nobody sees,
Much taller than those trees,
Up and up it goes,
Still it never grows?

How many sides does a circle have?

I am under you when I am whole.
I shift above you if you remove the first letter.
I come all around you if you remove the second as well.

Can you tell me who I am?

O_er_t_o_

Complete the missing letters of the given word.

Two in a corner, one in a room, zero in a house, but one in a shelter. What is it?

It is an eleven letter word.
The first, second, third and fourth letters form a banquet's name.
The fifth, sixth and seventh letters form a car's name.
The eighth, ninth, tenth and eleventh letters form a mode of transport.

Can you identify what word it is?