Find the next number in the sequence

1, 2, 6, 21, 88, __?

There is an English word that can be used up to four times in a row without modifying the spelling and form a valid grammatical sentence.

Do you know what word is that?

Can you decipher the two rows to find the hidden word?

Take 9 from 6, 10 from 9, 50 from 40, and leave 6.

How Come ??

Forwards I am heavy, backward I am not. What am I?

It belongs to you, but other people use it more than you do. What is it?

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?

In the below-given picture of a pretty girl, there is something wrong. Can you find out what it is?

There are 2 cops parked along a one-way street looking for traffic violations. They spot a taxi driver going in the wrong direction, yet they do nothing.

Why?

You are an expert on paranormal activity and have been hired to locate a spirit haunting an old resort hotel. Strong signs indicate that the spirit lies behind one of four doors. The inscriptions on each door read as follows:

Door A: It's behind B or C
Door B: Its behind A or D
Door C: It's in here
Door D: It's not in here

Your psychic powers have told you three of the inscriptions are false, and one is true. Behind which door will you find the spirit?