When it's bad luck to meet a black cat?

Can you arrange the six given marbles in a manner that each one of them is touching all four marbles of different colours?

The doctor advised his patient to take a tablet after every fifteen minutes. He gave him five tablets in total.

How much time will he take to have all the five tablets?

Replace the question mark with the number below given a simple math problem.

You see a boat filled with people, yet there isn’t a single person on board. How is that possible?

Can you solve the maths in the below-given picture equation?

You are in a room with no metal objects except for two iron rods. Only one of them is a magnet.
How can you identify which one is a magnet?

Things are just as they seem, right? Well, check again.
Can you count the number of tigers in this picture ?

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?

Many have heard it, but nobody has ever seen it, and it will not speak back until spoken to. What is it?