Which number should replace the question mark?

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

I have a hole in my back and legs I lack.
I live where I can’t breathe and I eat without teeth.
What am I?

Whats the next number in the below number sequence pattern.

13 decks of cards have been mixed. What is the minimum number of cards that must be taken out from the above-mixed cards to guarantee at least one 'four of a kind?

My friends called me Iron59 because my parents are a chemist and a mathematician. What is my real name?

What is the coolest letter in the alphabet?

Find The Next Number in this series.
1, 2, 6, 42, 1806 ?

There are 2 sand hourglasses.

The small one can measure 5 hours and the large one can measure 7 hours.

How can we measure 16 hours with 2 sand hourglasses running together ?

Can you find the six hidden animals in the picture below?