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

A boy and a girl are sitting on the porch.
"I'm a boy," says the child with black hair.
"I'm a girl," says the child with red hair.
If at least one of them is lying, who is which?

You are in a room that has three switches and a closed door. The switches control three light bulbs on the other side of the door. Once you open the door, you may never touch the switches again. How can you definitively tell which switch is connected to each of the light bulbs?

Two in a corner, one in a room, zero in a house, but one in a shelter. What is it?

By removing one matchstick and adding one matchstick, can you convert the word "ZOO" to an animal name?

'S' refers to the number of seconds in a day and 'H' refers to the number of hours in ten years. Which quantity out of these two is greater?

I am taken from a mine and shut up in a wooden case, from which I am never released, and yet I am used by almost every person. What am I?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

Why is a river so rich ?

How can you tell a raw egg from a hard-boiled egg?