Can you convert the number zero(0) into a positive number using just one mathematical operator ?

The doctor prescribed you to take one pill from the bottle every half an hour. The bottle is now left with only three pills.

How long do you think you have before you run out of pills?

A large water tank has two inlet pipes (a large one and a small one) and one outlet pipe. It takes 3 hours to fill the tank with the large inlet pipe. On the other hand, it takes 6 hours to fill the tank with the small inlet pipe. The outlet pipe allows the full tank to be emptied in 9 hours.

What fraction of the tank (initially empty) will be filled in 0.64 hours if all three pipes are in operation? Give your answer to two decimal places (e.g., 0.25, 0.5, or 0.75).

Can you find out what is missing?

1 3 5
2 4 ?

Hint: It's not six. Think out of the box.

what's the probability of getting a king or a queen from a pack of 52 cards?

You need to remove two matchsticks to make the below equation true. Can you do it ?

Who is that with a neck and no head, two arms and no hands? What is it?

A number with an interesting property:

When I divide it by 2, the remainder is 1.
When I divide it by 3, the remainder is 2.
When I divide it by 4, the remainder is 3.
When I divide it by 5, the remainder is 4.
When I divide it by 6, the remainder is 5.
When I divide it by 7, the remainder is 6.
When I divide it by 8, the remainder is 7.
When I divide it by 9, the remainder is 8.
When I divide it by 10, the remainder is 9.

It's not a small number, but it's not really big, either.
When I looked for a smaller number with this property I couldn't find one.

Can you find it?

I am quite hot but become too cold if you remove the first two letters. What am I?

What 4-letter word can be written forward, backward or upside down, and can still be read from left to right?