What is always in front of you but can’t be seen?

A number can be multiplied by multiple of nine
i.e 9 18 27 36 45 ...

and the resulting number consist of only one digit.

Can you identify the number ?

Why 1729 is a magic number? Answer Logically.

How many pluses should we put between the digits of 987654321 to get a total of 99, and where?

Why do we preferably have round manhole covers and not square ones?

0 0 0 = 6
1 1 1 = 6
2 2 2 = 6
3 3 3 = 6
4 4 4 = 6
5 5 5 = 6
6 6 6 = 6
7 7 7 = 6
8 8 8 = 6
9 9 9 = 6

You can use any mathematical symbols in the space provided to make all above algebraic expressions true.

You board a train. The train will have to enter a tunnel soon. You are claustrophobic. Which place is the best for you to sit?

The first person saw the bridge step on it and crossed,
the second person saw the bridge did not step on it but crossed,
the third person did not see the bridge did not step on it but crossed.
Who are these people?

The following four words might seem abrupt to you. But you can make them meaningful by just adding vowels.
RDSH
GGPLNT
TMT
NN

Hint: All of them are vegetables.

I have cities, but no houses. I have mountains, but no trees. I have water, but no fish. What am I?