How can you make number one disappear by adding something to it?

A detective visits his friend John just to discover that John's neighbour Dr Jacob was murdered. Dr Jacob, who is a mathematician wrote the murderer's name in a code word "Hcqtfz". There were five suspects
1. Ajit
2. Pankaj
3. Ganpat
4. Deenu
5. Hariya

The Detective was instantly able to find the murderer.
Can you?

If you remove one from eleven, it becomes ten. If you remove one from nine, it becomes ten.

How is this possible?

John left on a horse on Thursday , was gone for two days, and came back on Thursday after completing his work. How did that happen?

Can you find out the next digit in the following series ?

0, 0, 1, 3, 2, 6, 3, 9, 4, 12, 5, ?

I am a white box having no key or lid.
Yet there is a golden treasure inside it.

What Am I?

When 99 is considered higher than 100?

John enters a small room. The Door Closes.
When the door opens, John is in a larger room.

Explain?

The following question it puts forth you:

25 - 55 + (85 + 65) = ?

Then, you are told that even though you might think it's wrong, the correct answer is actually 5!

Whats your reaction to it? How can this be true?

An artist while painting a scenic beauty, decides to paint three layers of blue colour on the sky.

Which layer will go on the first?