What goes up but never comes down?

A mile-long train is moving at sixty miles an hour when it reaches a mile-long tunnel. How long does it take the entire train to pass through the tunnel?

How can you make the following equation true by drawing only one straight line: 5+5+5=550 ?

As a whole I am both
safe and secure.

Behead me and I become
a place of meeting.

Behead me again and I am
the partner of ready.

Restore me, and I become
the domain of beasts.

What am I?

Chhote se Chintu Miyan,
Lambi si Pooch.
Jahan Jaye Chintu Miyan,
Wahan Jaye Pooch.

छोटे से चींटू मियाँ,
लंबी सी पूंछ।
जहाँ जाये चींटू मियाँ,
वहाँ जाये पूंछ।

Bolo kya?

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

French Police inspects a room where there are no windows, no doors, no tables and is almost empty expect there is just a puddle of water. They found a dead man who obviously hung herself from the ceiling, but they are not able to figure out how this had happened.

John and Jacob entered the crime scene and easily able to solve the case.

How did the man die?

A tree doubled in height each year until it reached its maximum height over the course of ten years. How many years did it take for the tree to reach half its maximum height?

Find the next number in the series below.

6 18 270 72090 ?

I know a 5-digit number having a property that With a 1 after it, it is three times as large as it would be with a one before it.

Guess the number?