What number should come in place of the question mark below?

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?

Spelt forwards I’m what you do every day, spelled backwards I’m something you hate. What am I?

A man in a car saw a Golden Door, Silver Door and a Bronze Door. What door did he open first?

If nine thousand, nine hundred nine dollars is written as $9,909,
how should twelve thousand, twelve hundred twelve dollars be written?

I am not alive, but I grow; I don't have lungs, but I need air; I don't have a mouth, but water kills me. What am I?

Create a number using only the digits 4,4,3,3,2,2,1 and 1. So i can only be eight digits. You have to make sure the ones are separated by one digit, the twos are separated by two digits the threes are separated with three digits and the fours are separated by four digits

In the figure, you can see nine stars. What you have to do is connect all of them by using just four line and without lifting your hand i.e. in a continuous flow.

I possess a head

I flaunt a tail

But I don't have mouth or legs

Can you find out who I am?

What occurs twice in a week, once in a year but never in a day?