Solution:

The prisoner picks a marble and without showing it to anyone swallows it and then picks the remaining marble and shows to everyone which was black which proved the first marble prisoner pick must be white.
The Mad King has no option but to let the prisoner go.

Solution:

6

Explanation:
Key1: 3 attempts for 3 gates.
Key2: 2 attempts for remaining 2 gates.
Key3: 1 attempts for the last gate.

Solution:

19.

Note: Many of you have jumped to solution 21.

Solution:

February(just 28 days)

Solution:

Cup-8

Explanation:
This might be tricky for mobile users where the bottom cup is difficult to focus on.

Solution:

47.

Explanation:
Aarav is 6 years old and his sister Arshika is half of his age, which indicates Arshika age is 3 years less than Aarav's age. So when Aarav is 50, Arshika will be 47

Solution:

East

Explanation:
- Right Turn => North Direction
- About Turn => south Direction
- Left Turn => East Direction

Solution:

Sheldon filled a Mug with water and held it over his head for 10 minutes.

Solution:

Because Thibaut Courtois is goalkeeper(goal + keeper)

Solution:

0%. as it will be night in 72 hours and of course, there will be no sun