What four weights can be used to balance from 1 to 30 pounds?

What's the next in the series?

H, Be, F, S, Mn, Kr, In, Gd, Tl, ?

You need to pick one entry from pot A and one from pot B to have a perfect match. Can you do it?

An express train takes 3 seconds to enter the tunnel which is 1 km long.
If it is travelling at 120 km an hour, how long will it take to pass completely through the tunnel?

Which number should replace the question mark?

There are 20 people in an empty, square room. Each person has full sight of the entire room and everyone in it without turning his head or body, or moving in any way (other than the eyes). Where can you place an apple so that all but one person can see it?

The captain of a ship is telling you an interesting story and then poses a question. He says, “I have travelled the oceans far and wide. One time, two of my sailors were standing on opposite sides of the ship. One was looking west and the other one east. And at the same time, they could see each other clearly. Can you tell me how that was possible?”

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

You Throw The Outside, Cook The Inside
Eat The Outside, Throw The Inside.

What Is It?

Can anyone tell me a word in the English dictionary which has a silent 'z'?