What does this simple rebus mean?

Find The Next Number in this series.
1, 2, 6, 42, 1806 ?

This is a simple one. You just have to count the number of Fs in the given sentence.

Finished Files are the result of years of scientific study combined with the experience of years.

How many did you count?

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?

It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

what does this picture(rebus) riddle means ?

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?

Find the next number in the sequence

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

A landlord calls both of his sons and tells them that their horses will now decide who will transfer the inheritance. He tells them to race along the land till the end and the one whose horse will be slower will win and be the heir to all the property.

Both of them keep wandering for days but to no result. Then they ask a wise man regarding it. The man advises them on the matter after which they jump on the horses and race as fast as they can till the end. Why did they do it?

What did the wise man say?

You find yourself in a strange place guarded by two guards.One of the guard always say truth while other always lies.You don't know the identity of the two.You can ask only one question to go out from there. What should you ask?