Which number should replace the question mark?

I have a five and a three-gallon jar. Assuming there is an infinite supply of water, how can I measure one-gallon water?

John was visiting his friend Jacob. He found out that his friend's wife had just killed a burglar in self-defense.
John asks Jacob about what happened and he told that "His wife was watching television when suddenly the bell rang. She thought that it is her husband Jacob but she found the burglar who attacked her instantly and she got so frightened that she killed the burglar immediately with the knife.
John asked the police to arrest his friend's wife. Why?

A tourist visits a small town for his research. While in the town, he decides to get a haircut. Since the town is quite small, there are only two barbers in the town � one on the North Street and one on the South Street. The barbershop on the North Street is a mess and the barber has a weird and pathetic haircut. While the barbershop at the South Street is pretty tidy and the barber as well has an impressive haircut.

Which barbershop will the tourist visit for his haircut and why?

Why 1729 is a magic number? Answer Logically.

I sleep during the day and fly at night, but I have no feathers to aid my flight. What am I?

What demands an answer, but asks no questions

What 4-letter word can be written forward, backward or upside down, and can still be read from left to right?

what's the probability of getting a king or a queen from a pack of 52 cards?

Which digit occurred maximum times between the number 1 and 1000?