What 4-letter word can be written forward, backward or upside down, and can still be read from left to right?

Can you convert the number zero(0) into a positive number using just one mathematical operator ?

Which number comes next in the number series?

2, 9, 30, 93, ?

What you cannot hold but it is yours?

How can you throw a ball as hard as you can and have it come back to you even if it doesn't hit anything there is nothing attached to it and no one else catches or throws it.

What are the 50th, 63rd and 100th numbers in the sequence below?
4, 5, 8, 8, 9, 9, 12, 13, 13, 13, 17, 18, ...

There are people and strange monkeys on this island, and you can not tell who is who (Edit: until you understand what they said - see below). They speak either only the truth or only lies.
Who are the following two guys?
A: B is a lying monkey. I am human.
B: A is telling the truth.

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

What does this Rebus Picture mean?

In the city of Brain Teasers, 5% of people do not list their phone numbers. Now if we select random 100 people from the phone directory, then how many people selected will have unlisted phone numbers?