Replace the question mark with the number below given a simple math problem.

Is the statement valid that it does not matter how much older a sibling is, eventually the younger one will be half as old as the older one?

What does this rebus mean?

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One evening there was a murder in the home of a married couple, their son and daughter. One of these four people murdered one of the others. One of the members of the family witnessed the crime.

The other one helped the murderer.

These are the things we know for sure:

1. The witness and the one who helped the murderer were not of the same sex.

2. The oldest person and the witness were not of the same sex.

3. The youngest person and the victim were not of the same sex.

4. The one who helped the murderer was older than the victim.

5. The father was the oldest member of the family.

6. The murderer was not the youngest member of the family.

Who was the murderer?

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

There are two candles. Both will only burn exactly for an hour. How will you use these two candles to measure forty-five minutes?

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

Solve the counting riddle by identifying the number of triangles in the given picture.

How could a baby fall out of a twenty-story building onto the ground and live?

If,
29 - 1 = 30
9 - 1 = 10
14 - 1 = 15

Based on similar logic, Can you prove that the below algebraic equation is true?
11 - 1 = 10 ?