What's the next in the series?

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

If,

A + B = C
D - C = A
E - B = C

Based on the above equations, find out the answer for:

D + F = ?

What can run but never walks, has a mouth but never talks, has a head but never weeps, has a bed but never sleeps?

You need to complete the maze by entering from the entrance marked below in the figure near the yellow circle, bottom left and leaving from the exit point near the green circle, bottom middle.

Rule of Game: You can move only by exchanging green and yellow circles.

Twice ten are six of us,

Six are but three of us,

Nine are but four of us;

What can we possibly be?

Would you know more of us?

Twelve are but six of us,

Five are but four, do you see?

What are we?

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

If a wheel has 54 spokes, how many spaces are there between the spokes?

I am the beginning of the end, and the end of time and space. I am essential to creation, and I surround every place. What am I?

A woman lives in a Tall building thirty-six floors high and served by several elevators which stop at each floor going up and down. Each morning she leaves her apartment and goes to one of the elevators. Whichever one she takes is three times more likely to be going up than down. Why?

You have a three-gallon and a five-gallon measuring device. You wish to measure out four gallons.