What four weights can be used to balance from 1 to 30 pounds?

A King wants to send the diamond ring to his girlfriend securely. He got multiple locks and their corresponding keys. His girlfriend does not have any keys to these locks and if he sends the key without a lock, the key can be copied in the way. How can King send the ring to his girlfriend securely?

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

which number am I?

There was once a college that offered a class on probability applied to the real world. The class was relatively easy, but there was a catch. There were no homework assignments or tests, but there was a final exam that would have only one question on it. When everyone received the test paper it was a blank sheet of paper with a solitary question on it: 'What is the risk?'.Most students were able to pass, but only one student received 100% for the class! Even stranger was that he only wrote down one word!
What did he write?

By including only four matchsticks in below picture, you have to make "Four Triangles And Two Squares"

What is the difference between a jeweller and a jailer?

What three numbers, none of which is zero, give the same result whether they’re added or multiplied?

Why is the Hole below a Lock?

What is black when you buy it, red when you use it, and gray when you throw it away?

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?