Find the Next Number in the Sequence

2 9 3 1 8 4 3 6 5 7 ?

An infinite number of mathematicians are standing behind a bar. The first asks the barman for half a pint of beer, the second for a quarter pint, the third an eighth, and so on. How many pints of beer will the barman need to fulfill all mathematicians' wishes?

How many triangles can you find in this given picture?

Jessica is telling her friends this story and asks them to guess if it’s the truth or a lie: “There was a man sitting in a house at night that had no lights on at all. There was no lamp, no candle, and no other source of light. Yet, he sat in the house and read his book happily.” Her friends say she’s lying, but Jessica corrects them and says she’s telling the truth. Jessica’s story is true—but how?

What has no start, end, or centre?

No one wants to have it, but if one got it, he does not want to lose it. What is It?

A boy was at a carnival and went to a booth where a man said to the boy, "If I write your exact weight on this piece of paper then you have to give me $50, but if I cannot, I will pay you $50." The boy looked around and saw no scale so he agrees, thinking no matter what the carny writes he'll just say he weighs more or less. In the end the boy ended up paying the man $50. How did the man win the bet?

Find the combined weight of the Cat, Dog and Rabbit in the given picture.

In 1990, a person is 15 years old. In 1995, that same person is 10 years old. How can this be?

I know a ten-letter word in the English language which can be typed using only the top rows of the computer keyboard.