What occurs twice in a week, once in a year but never in a day?

What is the coolest letter in the alphabet?

I possess a head

I flaunt a tail

But I don't have mouth or legs

Can you find out who I am?

John is the son of Jacob.
So,
Jacob is the_____of John's father?

Its something that each of us devours,
Not just us but birds, beats, trees, and flowers,
Frets iron and nibbles steel,
Toil hard stones to meal,
Exterminates king, collapse town,
And blows the mountains down.

Given that

(78)^9 = 6
And (69)^4 = 11

Can you find out

(99)^2 =?

(Note: This is Logical, not Mathematical)

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?

You are in a room that has three switches and a closed door. The switches control three light bulbs on the other side of the door. Once you open the door, you may never touch the switches again. How can you definitively tell which switch is connected to each of the light bulbs?

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

What has to be broken before you can use it?