If two's company, and three's a crowd, then whats four and five ?

13 decks of cards have been mixed. What is the minimum number of cards that must be taken out from the above-mixed cards to guarantee at least one 'four of a kind?

The first person saw the bridge step on it and crossed,
the second person saw the bridge did not step on it but crossed,
the third person did not see the bridge did not step on it but crossed.
Who are these people?

There is something which you can be arrested for attempting but not for successfully completing.

Prove that the below maths equation is true.

8 + 8 = 91

Can you quickly find which two matchstick figures are identical?

If it took eight men ten hours to build a wall, how long would it take four men to build it?

What brings you down but never up?

What comes
Once in a Year
Twice in a Month
4 times in a Week
6 times in a Day

I am first found in caves, now prolific online; I am a depiction, a drawing, a symbol, or sign. I will convey whichever mood you could wish; or for that matter, a fist, flask, or fish. What am I?