Sherlock Holmes was challenged to make a pre-drawn line smaller without erasing it. He did it in fractions of seconds. How?

what one word does the below rebus identifies?

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

What is the riddle which can be asked all day with a different correct answer each time.

An exterior architect is asked by a builder to plant seven trees in a manner that there are exactly six rows of trees in a straight line and each row has three trees in particular.

How will he do it?

Before Mount Everest was discovered, what was the highest mountain in the world?

The host of a game show, offers the guest a choice of three doors. Behind one is a expensive car, but behind the other two are goats.
After you have chosen one door, he reveals one of the other two doors behind which is a goat (he wouldn't reveal a car).

Now he gives you the chance to switch to the other unrevealed door or stay at your initial choice. You will then get what is behind that door.

You cannot hear the goats from behind the doors, or in any way know which door has the prize.

Should you stay, or switch, or doesn't it matter?

A man has a barrel filled with oil that weighs 100 pounds, and then he puts something into it. Now the barrel weighs less than 100 pounds. What did he put in the barrel?

What can run but never walks, has a mouth but never talks, has a head but never weeps, has a bed but never sleeps?

This puzzle is for Harry Potter fans. Do you know why Tom Riddle is called Lord Voldemort?