Can you replace the question mark with the correct number?

If it took eight men ten hours to build a wall, how long would it take four men to build it?

What does a man do only once in his lifetime, but women do once a year after they are 29?

Using four sevens (7) and a one (1) create the number 100. Except for the five numerals, you can use the usual mathematical operations (+, -, x, :), root and brackets ()

There are 20 people in an empty, square room. Each person has full sight of the entire room and everyone in it without turning his head or body, or moving in any way (other than the eyes). Where can you place an apple so that all but one person can see it?

What do you think with the below Picture ?

You walk into a room that contains a match, a kerosene lamp, a candle and a fireplace. What would you light first?

On rolling two dices (six-sided normal dice) together, what is the probability that the first one comes up with a 2 and the second one comes up with a 5?

Sachin bought a car with a strange 5 digit numbered plate.The water image of the number is 78633 more than my car number. All the digits of car number are distinct.

What is the original number on number plate?

It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?