Count the squares in the matchstick puzzle below?

A donkey is behind another donkey
I'm behind that second donkey
But there is a whole nation behind me

It is a murder you can describe in a word.

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 ?

A boy and his father are caught in a traffic accident, and the father dies. Immediately the boy is rushed to a hospital, suffering from injuries. But the attending surgeon at the hospital, upon seeing the boy, says 'I cannot operate. This boy is my son.' How is this situation explained?

Which is Odd One Out and why?

4377

3954

9862

8454

9831

100 prisoners are stuck in the prison in solitary cells. The warden of the prison got bored one day and offered them a challenge. He will put one prisoner per day, selected at random (a prisoner can be selected more than once), into a special room with a light bulb and a switch which controls the bulb. No other prisoners can see or control the light bulb. The prisoner in the special room can either turn on the bulb, turn off the bulb or do nothing. On any day, the prisoners can stop this process and say "Every prisoner has been in the special room at least once". If that happens to be true, all the prisoners will be set free. If it is false, then all the prisoners will be executed. The prisoners are given some time to discuss and figure out a solution. How do they ensure they all go free?

What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

Which five letter word can be added at the end of below word to form a
valid word?

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Can you find the next number in the below sequence
3 , 7 , 10 , 11 , 12 , 17 ?

Assume there are approximately 5,000,000,000 (5 billion) people on Earth. What would you estimate to be the result, if you multiply together the number of fingers on every person's left hand? (For the purposes of this exercise, thumbs count as fingers, for five fingers per hand.) If you cannot estimate the number then try to guess how long the number would be.