I have no doors but I have keys, I have no rooms but I have space, you can enter but you can’t leave! What am I?

A man dies of old age on his 25 birthday. How is this possible?

Decode below rebus
D
N
A
T
S , D

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?

using four eights (8) and a one (1) and one mathematical symbol , create the number 100

Complete the table series riddle by finding the number that can replace "??".

You have two buckets - one holds exactly 5 gallons and the other 3 gallons. How can you measure 4 gallons of water into the 5 gallon bucket?

(Assume you have an unlimited supply of water and that there are no measurement markings of any kind on the buckets.)

In a classic wine shop, the list of three most popular wines are:
- The cost of 1 French wine bottle: 500$
- The cost of 1 German wine bottle: 100$
- The cost of 20 Dutch wine bottles: 100$

John entered the wine shop and he needs to buy
- All three types of wine bottles.
- Needs to buy Dutch wine bottles in multiples of 20.
- Need to buy 100 wine bottles in total.

John has only 10000$. How many wine bottles of each type, John must buy?

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

What is the riddle which can be asked all day with a different correct answer each time.