Riddle:
If you go to the movies and you're paying, is it cheaper to take one friend to the movies twice, or two friends to the movies at the same time?
Answer: It's cheaper to take two friends at the same time. In this case, you would only be buying three tickets, whereas if you take the same friend twice you are buying four tickets.
Riddle:
A tree doubled in height each year until it reached its maximum height over the course of ten years. How many years did it take for the tree to reach half its maximum height?
Riddle:
I am a word of five letters. Take away my first and I am the name of what adorns the estate of many of the nobility of England. Take away my first and second, and I am the name of a place where all the world was once congregated. Take away my last, and I am the name of a beautiful mineral. Take away my two last, and I am the name of a fashionable place of resort. I am small in stature but capable of doing a great deal of mischief, as I once did in London in the year 1666. What word am I?