Many have heard it, but nobody has ever seen it, and it will not speak back until spoken to. What is it?

When we see 2 but call 10?

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?

You and your two friends are working in a multinational company. How can you three find out the average salary of you all without disclosing your own salary to the other two?

Irene killed hundreds of people mercilessly and yet the police were not able to put her behind the bars. Why?

I sleep during the day and fly at night, but I have no feathers to aid my flight. What am I?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

Can you find out who is the kidnapper in below Picture and why, Explain ?

Replace all '*' with digits 1, 2, 3, 4, 5 and 6 to make below statement true.

* *
x *
=====
* * *

A donkey is behind another donkey
I'm behind that second donkey
But there is a whole nation behind me

It is a murder you can describe in a word.