What always comes into a house through the keyhole?

A rubber ball keeps on bouncing back to 2/3 of the height from which it is dropped. Can you calculate the fraction of its original height that the ball will bounce after it is dropped and it has bounced four times without any hindrance ?

What three numbers, none of which is zero, give the same result whether they’re added or multiplied?

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?

I know a country, If you remove the last alphabet of its name, it will become a part of your body. Do you name it?

Analyze and find the missing item in the sequence:
16, 06, 68, 88, __, 98

If eleven plus two equals one, what does nine plus five equal?

Count the squares in the matchstick puzzle below?

I am the one who remains awake when you sleep. But I need to rest when you awake. Who Am I?

John was born on March 5, 1970, in Delhi, India. Jacob was born 25 days before John. The year when they took birth, Republic Day fell on Monday.

Can you find out on what day was Jacob born?