What is at the end of a rainbow?

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

Which is faster, Heat or Cold ? Explain.

What is both possible and impossible at the same time?

Things are just as they seem, right? Well, check again.
Can you count the number of tigers in this picture ?

Mr Black, Mr Gray, and Mr White are fighting in a truel. They each get a gun and take turns shooting at each other until only one person is left. Mr Black, who hits his shot 1/3 of the time, gets to shoot first. Mr Gray, who hits his shot 2/3 of the time, gets to shoot next, assuming he is still alive. Mr White, who hits his shot all the time, shoots next, assuming he is also alive. The cycle repeats. If you are Mr Black, where should you shoot first for the highest chance of survival?

What's a single-digit number with no value?

What goes up but never comes down?

There are hundred red gems and hundred blue gems. The blue gems are priceless while the red gems equal wastage. You have two sacks one labeled Heads and the other Tails. You have to distribute the gems as you want in the two sacks. Then a coin will be flipped and you will be asked to pick up a gem randomly from the corresponding sacks.

How will you distribute the gems between the sacks so that the odds of picking a Blue gem are maximum?

In two decks of cards, what is the least amount of cards you must take to be *guaranteed* at least one four-of-a-kind?