What goes up but never comes down?

Find the Next Number in the Sequence

2 9 3 1 8 4 3 6 5 7 ?

I have Rs.50 and I spend it in the way as below.

The square root of number 121 is "11". What is the square root of the number "12345678987654321."?

What has six faces, but does not wear makeup, has twenty-one eyes, but cannot see?

When is the top of a mountain similar to a savings account?

I come in different shapes and sizes.
Parts of me are curved, other parts are straight.
You can put me anywhere you like,
but there is only one right place for me.
What am I?

A girl was sitting in her hotel room when she heard a knock on the door. She opened the door and found that a man was standing outside. The man said, "Oh! I am really sorry, I thought this was my room." He then walked through the corridor to the elevator. The girl did not know the man. She closed her door and called security asking them to apprehend the man. What made her suspicious of that man? He might have been genuinely mistaken.

What Time Should the last watch show in the below figure?

A pond had 60 fish, out of which, all but 20 died.
How many fishes are now present in that pond?