P is the father of Q and S is the son of R. T is the brother of P and has a daughter U. If R is the sister of P, then what is the relation between U, Q and S?

Can you arrange four 9's and use at most 2 math symbols, to make the total 100?

A train leaves from point A for point B at 80 mph. After half an hour, another train leaves from point B for point A at 60 mph.

Which of the trains will be farther from point A when they meet ?

In four steps you need to move the word 'cold' From 'warm' by replacing one alphabet at a time such that every word formed at each step is acceptable in English Dictionary.

How many times can you subtract the number 5 from 25?

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.

In the picture given below, can you find out which digit will take place of the question mark?

Three doctors said that Bill was their brother. Bill says he has no brothers. How many brothers does Bill actually have?

What is the next number in this series?

4,12,84,3612....

What is black when you buy it, red when you use it, and gray when you throw it away?