What goes up but never comes down?

Which is faster, Heat or Cold ? Explain.

There was an aeroplane crash, every single person died, but two people survived. How is this possible?

What is wrong in the below Picture?

Can you replace the X (both small and big x) with the numbers between 1 to 19 such that all the rows of 3 numbers between X (big x) sum to 23?

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

In the Wild West, you are challenged into a death match by two bounty hunters nicknamed Golden Revolver (GR) and Killer Boots (KB). You accept the challenge. None of you want to waste any of the bullet and so a certain rules are laid down:

1) All of you will shoot in a given order till the last man standing.
2) Each of you shoots only once upon his turn.
3) If any one of you is injured, the other two will finish him off with an iron rod.
4) The worst shooter of all (which is you) shoots first and the best one shoots at the last.

Now, how will you plan things if you know that you hit every third shot of yours, KB hits every second shot and GR hits every shot ?

A Doctor always sneezes before the rain. Doctor sneezes, Will it rain?

You want to boil a two-minute egg. If you only have a three-minute timer (hourglass), a four-minute timer and a five-minute timer, how can you boil the egg for only two minutes?

O_er_t_o_

Complete the missing letters of the given word.