What always comes into a house through the keyhole?

A beggar on the street can make one cigarette out of every 6 cigarette butts he finds. After one whole day of searching and checking public ashtrays the beggar finds a total of 72 cigarette butts. How many cigarettes can he make and smoke from the butts he found?

It's a protector.
It sits on a bridge.
One individual can see directly through it, while others wonder what it hides.

What is it?

I am a prime number.
The double of myself is equal to the square of me.

which number am I?

In a jungle where there are no street lights or any other artificial source of lights, I notice a black snake crossing the road.
How did I get sight of the snake?

Find out the missing number in the picture attached:

Three men in a cafe order a meal the total cost of which is $15. They each contribute $5. The waiter takes the money to the chef who recognises the three as friends and asks the waiter to return $5 to the men.

The waiter is not only poor at mathematics but dishonest and instead of going to the trouble of splitting the $5 between the three he simply gives them $1 each and pockets the remaining $2 for himself.

Now, each of the men effectively paid $4, the total paid is therefore $12. Add the $2 in the waiters pocket and this comes to $14. Where has the other $1 gone from the original $15?

A spy was in Canada trying to steal insider information on how to set up new Maple Syrup factories in their country. He was introduced to the operations manager of the biggest factory in Canada. However, the manager was suspicious and decided to test him with a question before he trusted him. So he asked, “What would you be sure to find in the middle of Toronto?” The spy thought fast and came up with an answer for the manager. What was his answer?

You need to arrange three 7 and mathematical symbols to form number 1?

Why do you find that most of the buildings are deprived of the 13th floor?