The centre of the third figure is empty. What digit should fit inside?

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?

Replace the question mark with the correct number.

2 + 2= 4
3 + 3= 18
4 + 4= 48
5 + 5= ?

In the city of Brain Teasers, 5% of people do not list their phone numbers. Now if we select random 100 people from the phone directory, then how many people selected will have unlisted phone numbers?

Astrology starts with the alphabet A, Biology starts with B, Psychology with P and Limnology with L.

Can you find an "ology" that begins with a P?

What you cannot hold but it is yours?

Your mother’s brother’s only brother-in-law is asleep on your couch. Who is asleep on your couch?

What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

Can you find a pattern and the missing number in the series given below?

100, 155, 258,? , 584, 819.

Can you count the number of quadrilaterals in the picture below?