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

The host of a game show offers the guest a choice of three doors. Behind one is an 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?

What mathematical symbol can be put between 5 and 9, to get a number bigger than 5 and smaller than 9?

My first is in chocolate but not in ham. My second is in cake and also in jam. My third at tea time is easily found. Altogether, this is a friend who is often around. What is it?

Why do we preferably have round manhole covers and not square ones?

I have an eye but still cannot see.

Who am I?

Can you find the dog hidden in a group of pandas?

A bomb exploded in a room full of married couples and no one died. How?

What has many teeth, but cannot bite?

How much will a 38° angle measure when looked at under a microscope that magnifies ten times?